feat: publish av-tools 0.2.0

2026-07-27 01:04:21 +02:00
68 changed files with 4130 additions and 605 deletions
--- a/.gitignore
+++ b/.gitignore
@@ -11,10 +11,12 @@ node_modules
 dist
 dist-ssr
 release
+.core-build
 test-results
 playwright-report
 coverage
 public/vendor/ffmpeg
+vendor/*.tmp
 *.local

 # Editor directories and files
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,31 @@
 All notable changes to av-tools are documented here. The project follows
 semantic versioning once a first release is legally publishable.

+## 0.2.0 — 2026-07-27
+
+- Allow recognized local audio/video to begin native browser playback while
+  FFmpeg inspection continues in the background.
+- Replace the fixed 30-second media-inspection watchdog with a bounded,
+  size-aware budget and report timeout expiry separately from user
+  cancellation.
+- Add an isolated, reproducible Chromium ST/MT Opus regression harness using
+  the reviewed cores, checked tone fixture and real built-in command plan.
+- Rebuild ST/MT core 0.12.10 with the upstream 5 MiB stack fix, lock and
+  deterministically package the exact assets, pass non-empty Opus encode and
+  re-probe in both modes, and enable Opus presets behind runtime capabilities.
+- Add bounded 0.04–10 second audio/video crossfades to normalized sequential
+  joins, including runtime `xfade`/`acrossfade` gates and clip-material checks.
+- Add bounded scene-change analysis and exact-PTS thumbnail/contact-sheet
+  extraction, with an honest no-scenes result instead of silent substitution.
+- Bundle unmodified DejaVu Sans 2.37 with byte identity, upstream archive
+  provenance and full terms; verify it in-browser before labelled contact
+  sheets and fail closed when `drawtext` is unavailable.
+- Add native execution coverage, pinned-core browser matrix steps and an opt-in
+  large-file browser playback-during-inspection evidence run.
+- Make removal of queued or active source inspections generation-safe, cancel
+  owned active probes and prevent stale results from updating deleted or
+  same-ID replacement assets.
+
 ## 0.1.0 — 2026-07-24

 - Scaffold a local-first React/Vite audio and video toolbox application.
--- a/LICENSES/DEJAVU_FONTS.txt
+++ b/LICENSES/DEJAVU_FONTS.txt
@@ -0,0 +1,92 @@
+Fonts are (c) Bitstream (see below). DejaVu changes are in public domain.
+Glyphs imported from Arev fonts are (c) Tavmjong Bah (see below).
+
+Bitstream Vera Fonts Copyright
+------------------------------
+
+Copyright (c) 2003 by Bitstream, Inc. All Rights Reserved. Bitstream Vera is
+a trademark of Bitstream, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of the fonts accompanying this license ("Fonts") and associated
+documentation files (the "Font Software"), to reproduce and distribute the
+Font Software, including without limitation the rights to use, copy, merge,
+publish, distribute, and/or sell copies of the Font Software, and to permit
+persons to whom the Font Software is furnished to do so, subject to the
+following conditions:
+
+The above copyright and trademark notices and this permission notice shall
+be included in all copies of one or more of the Font Software typefaces.
+
+The Font Software may be modified, altered, or added to, and in particular
+the designs of glyphs or characters in the Fonts may be modified and
+additional glyphs or characters may be added to the Fonts, only if the fonts
+are renamed to names not containing either the words "Bitstream" or the word
+"Vera".
+
+This License becomes null and void to the extent applicable to Fonts or Font
+Software that has been modified and is distributed under the "Bitstream
+Vera" names.
+
+The Font Software may be sold as part of a larger software package but no
+copy of one or more of the Font Software typefaces may be sold by itself.
+
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF COPYRIGHT, PATENT,
+TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL BITSTREAM OR THE GNOME
+FOUNDATION BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, INCLUDING
+ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
+THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM OTHER DEALINGS IN THE
+FONT SOFTWARE.
+
+Except as contained in this notice, the names of Gnome, the Gnome
+Foundation, and Bitstream Inc., shall not be used in advertising or
+otherwise to promote the sale, use or other dealings in this Font Software
+without prior written authorization from the Gnome Foundation or Bitstream
+Inc., respectively. For further information, contact: fonts at gnome dot
+org.
+
+Arev Fonts Copyright
+------------------------------
+
+Copyright (c) 2006 by Tavmjong Bah. All Rights Reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the fonts accompanying this license ("Fonts") and associated
+documentation files (the "Font Software"), to reproduce and distribute
+the modifications to the Bitstream Vera Font Software, including without
+limitation the rights to use, copy, merge, publish, distribute, and/or sell
+copies of the Font Software, and to permit persons to whom the Font Software
+is furnished to do so, subject to the following conditions:
+
+The above copyright and trademark notices and this permission notice shall
+be included in all copies of one or more of the Font Software typefaces.
+
+The Font Software may be modified, altered, or added to, and in particular
+the designs of glyphs or characters in the Fonts may be modified and
+additional glyphs or characters may be added to the Fonts, only if the fonts
+are renamed to names not containing either the words "Tavmjong Bah" or the
+word "Arev".
+
+This License becomes null and void to the extent applicable to Fonts or Font
+Software that has been modified and is distributed under the "Tavmjong Bah
+Arev" names.
+
+The Font Software may be sold as part of a larger software package but no
+copy of one or more of the Font Software typefaces may be sold by itself.
+
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF COPYRIGHT, PATENT,
+TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL TAVMJONG BAH BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, INCLUDING ANY GENERAL, SPECIAL, INDIRECT,
+INCIDENTAL, OR CONSEQUENTIAL DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT
+OR OTHERWISE, ARISING FROM, OUT OF THE USE OR INABILITY TO USE THE FONT
+SOFTWARE OR FROM OTHER DEALINGS IN THE FONT SOFTWARE.
+
+Except as contained in this notice, the name of Tavmjong Bah shall not be
+used in advertising or otherwise to promote the sale, use or other dealings
+in this Font Software without prior written authorization from Tavmjong Bah.
+For further information, contact: tavmjong @ free . fr.
--- a/LICENSES/README.md
+++ b/LICENSES/README.md
@@ -13,9 +13,8 @@ or patent considerations of bundled third-party components.
  `v12.15` source at revision
  `71aa99d37c02a7b4c435275ca9ef50e612f6efa1`; it covers the wrapper/util
  source.
- `GPL-2.0-or-later.txt` reproduces GNU GPL version 2. The published
-  `@ffmpeg/core` and `@ffmpeg/core-mt` 0.12.10 package manifests declare
-  `GPL-2.0-or-later`; “or later” comes from those manifests. The legal code
+- `GPL-2.0-or-later.txt` reproduces GNU GPL version 2 for GPL-enabled FFmpeg
+  and linked GPL components in the reviewed WebAssembly cores. The legal code
  was checked against the standard GPL-2.0 text in the installed Freedesktop
  SDK licence corpus and the SPDX licence-list text.
 - `CC0-1.0.txt` applies only to generated bytes under
--- a/README.md
+++ b/README.md
@@ -8,8 +8,8 @@ telemetry, runtime CDN, remote-media fetch or third-party script.
 It is also a Toolbox SDK application. The same static build runs directly or
 under Toolbox Portal with shared shell, theme, help and app switching.

-> **Release status:** 0.1.0 is licensed GPL-3.0-or-later. Its canonical
-> release consists of the exact reviewed `v0.1.0` source, production
+> **Release status:** 0.2.0 is licensed GPL-3.0-or-later. Its canonical
+> release consists of the exact reviewed `v0.2.0` source, production
 > ZIP/checksum and Corresponding Source bundle published together. See
 > [Licensing](#licensing).

@@ -23,7 +23,7 @@ Two workflows keep the product intentionally smaller than a nonlinear editor:
 - **Edit:** a media bin and sequential non-overlapping clip timeline with
  non-destructive settings, one export at a time.

-The planned 0.1 line covers typed/capability-gated conversion and remux,
+The 0.2 release covers typed/capability-gated conversion and remux,
 fast/accurate trim, split, compatible/normalized concatenate, reorder, crop,
 resize, frame-rate change, audio extraction/stream removal, waveform,
 peak/two-pass loudness normalization, gain, audio/video fades, metadata,
@@ -34,10 +34,18 @@ diagnostics and explicit browser export.
 The Edit workspace now exposes structural exports directly: fast stream-copy
 or preset-backed accurate trim uses the selected clip's timeline range, while
 fast concatenate requires explicit compatibility diagnostics and normalized
-concatenate requires a preset plus an explicit missing-audio policy.
+concatenate requires a preset plus an explicit missing-audio policy. Normalized
+joins can apply a uniform, capability-gated 0.04–10 second audio/video
+crossfade at every edit, with clip-material checks before queueing.
 Operations enter a bounded, in-memory application queue with at most eight
 scheduled operations and one FFmpeg execution at a time.

+Thumbnail series and contact sheets support even, interval, chapter, marker or
+bounded scene-change selection. Scene analysis records exact source
+presentation timestamps before extraction. Contact-sheet labels use only the
+bundled, SHA-256-verified DejaVu Sans 2.37 file and remain disabled unless the
+active core exposes `drawtext`; there is no remote/system-font fallback.
+
 When a source cannot be played directly, the preview panel can create a
 disposable H.264/AAC MP4 proxy. The user can bound it to 1–300 seconds and
 choose a maximum width from 480–1920 pixels. A proxy is reused from the local
@@ -53,14 +61,15 @@ Exact runtime packages:

 - `@ffmpeg/ffmpeg` 0.12.15;
 - `@ffmpeg/util` 0.12.2;
- `@ffmpeg/core` 0.12.10 (single-thread);
- `@ffmpeg/core-mt` 0.12.10 (multithread).
+- reviewed FFmpeg core build `0.12.10-reviewed-stack5m.1` in single-thread and
+  multithread profiles.

-The published cores contain **FFmpeg n5.1.4** (libavcodec 59.37.100), built
+The reviewed cores contain **FFmpeg n5.1.4** (libavcodec 59.37.100), built
 with x264, x265, libvpx, LAME, Ogg/Theora/Opus/Vorbis, zlib, libwebp,
 FreeType/FriBidi/HarfBuzz/libass and zimg. Both ~32 MiB WASM cores and their
-JS/worker files are copied from exact npm packages and served from the app's
-own origin. `npm run build` does not download them.
+JS/worker files are verified against a tracked build lock, unpacked from a
+deterministic repository artifact and served from the app's own origin.
+`npm run build` does not download them.

 Every engine load queries actual demuxers, muxers, decoders, encoders and
 filters. Presets remain disabled when requirements are absent; an extension or
@@ -92,10 +101,12 @@ WebM/VP8/Vorbis, MP3 and WAV are common preview candidates, but actual codec,
 browser and platform support is checked at runtime. Matroska and many other
 valid outputs may be download-only. A preview proxy may require re-encoding.

-The pinned core has an unresolved Opus encoding regression risk (zero-byte or
-out-of-bounds behavior reported around upstream stack-size fixes). Opus
-presets must stay unavailable unless a real non-empty, re-probeable ST/MT smoke
-passes. Details are in [FFmpeg build](docs/FFMPEG_BUILD.md).
+The 2026-07-26 Chromium regression harness ran the real built-in `audio-opus`
+plan against both reviewed cores. Each selected the requested ST/MT mode,
+produced non-empty Opus and passed codec/duration re-probing. Opus presets are
+therefore enabled when runtime capability discovery also succeeds. Exact
+commands and evidence boundaries are in
+[FFmpeg build](docs/FFMPEG_BUILD.md).

 ## Execution modes

@@ -169,9 +180,14 @@ Core assets are generated local build inputs:

 ```sh
 npm run vendor:ffmpeg
-npm run vendor:verify
+npm run vendor:verify-runtime
 ```

+The runtime verifier checks the tracked deterministic core artifact, source
+lock, build driver and generated same-origin files. The stricter
+`npm run vendor:verify` publication gate additionally requires and hashes the
+ignored Corresponding Source archive generated by `npm run source:package`.
+
 Regenerate or verify the tiny synthetic fixtures:

 ```sh
@@ -183,7 +199,7 @@ npm run fixtures:verify

 ```sh
 npm run manifest:check
-npm run vendor:verify
+npm run vendor:verify-runtime
 npm run typecheck
 npm run lint
 npm run format:check
@@ -191,6 +207,8 @@ npm test
 npm run build
 npm run toolbox:check
 npm run test:browser
+npm run evidence:large-preview # set AV_TOOLS_LARGE_MEDIA first
+npm run evidence:opus
 ```

 `npm run check` combines the non-browser production checks. Browser tests cover
@@ -198,13 +216,27 @@ the real pinned cores, MT-to-ST fallback, cancellation/recovery, generated
 fixtures, nested deployment, Toolbox context and the absence of runtime CDN
 traffic.

-The latest recorded local Vitest run on 2026-07-24 completed **303 passing
-tests and one conditional skip**. It includes broad structured-command
-execution against native FFmpeg 7.1.3; the skipped native subtitle burn-in case
-requires a `subtitles` filter unavailable in that host build.
+`npm run evidence:opus` independently contains each ST/MT browser process,
+prints one JSON report and exits normally even when the result is unsafe.
+`npm run test:opus-regression` runs the same evidence as the positive Opus
+enablement gate and exits nonzero unless both modes produce non-empty,
+re-probeable Opus. It is a mandatory release gate for the reviewed core
+profile.
+
+`AV_TOOLS_LARGE_MEDIA=/absolute/video.mp4 npm run evidence:large-preview`
+performs the opt-in large-file regression: the native video element must mount
+and advance before bounded inspection finishes, remain the same element after
+the authoritative probe completes and produce no browser error.
+
+The latest recorded local Vitest run on 2026-07-26 completed **313 passing
+tests and two conditional skips**. It includes broad structured-command
+execution against native FFmpeg 7.1.3; the skipped native subtitle burn-in and
+labeled contact-sheet cases require `subtitles` and `drawtext` filters that are
+unavailable in that host build.

 The Chromium suite exercises the pinned ST core across conversion,
-trim/concat/split, analysis, waveform, image, metadata, chapter, subtitle,
+trim/concat/split, bounded crossfades, analysis, waveform, scene-selected image
+generation, bundled-font contact-sheet labels, metadata, chapter, subtitle,
 queue and recovery workflows. The MT core is directly initialized and queried,
 and completes a real non-empty, re-probeable H.264/AAC conversion; the same
 path is benchmarked with 2-second 160×90 and 6-second 640×360 inputs. Nested
@@ -243,12 +275,12 @@ repository and the `GPL-3.0-or-later` SPDX licence.

 Portal must consume an independently built ZIP; it must not build or import
 av-tools source. Immutable Portal revision
-`bda9da044d61c109afd9969d357cc27f76648938` has isolation and WASM CSP
-permissions but lacks `media-src blob:`, which blocks Blob previews. The
-developer's active Toolbox Portal worktree currently contains the narrow local
-`media-src 'self' blob:` patch; that uncommitted worktree state does not change
-the immutable reference or release evidence. The exact distinction, smallest
-change and fallback are documented in
+`5c052bc6d1073a66600cfddc44c0e16da34bede8` (`v0.6.0`) provides the required
+isolation, narrow WebAssembly CSP, Blob media policy and explicit WASM MIME
+mapping. The active Portal worktree additionally extends immutable caching to
+the exact reviewed FFmpeg build profile without accepting mutable-looking
+suffixes. Its exact reviewed and staged
+boundaries are documented in
 [Portal requirements](docs/PORTAL_REQUIREMENTS.md).

 ## Release
@@ -272,11 +304,11 @@ metadata:
 ```sh
 npm run package:release
 npm run portal:smoke -- \
-  --allow-known-header-gap
+  --portal-root ../toolbox-portal
 ```

-The header-gap override remains development-only until the Portal CSP change is
-committed. Full commands and safety behavior are in
+The smoke harness clones the selected Portal `HEAD`; it never consumes
+uncommitted Portal files silently. Full commands and safety behavior are in
 [release documentation](docs/RELEASE.md).

 ## Licensing
@@ -286,11 +318,11 @@ and licensed **GPL-3.0-or-later**. See [LICENSE](LICENSE). The application
 provides a visible licence, source and no-warranty notice in its Help dialog.
 Third-party components retain their copyright and licence terms.

-The wrapper/util are MIT. Core/core-mt 0.12.10 declare
-GPL-2.0-or-later and statically include FFmpeg/external codec code with
-additional terms. The branch-based x264/LAME inputs have been resolved to
-immutable commits in the source record. A binary publication must include
-equivalent access to the reviewed Corresponding Source and notices. See:
+The wrapper/util are MIT. The reviewed 0.12.10 cores statically include
+GPL-enabled FFmpeg/external codec code with additional terms. The branch-based
+x264/LAME inputs have been resolved to immutable commits in the source record.
+A binary publication must include equivalent access to the reviewed
+Corresponding Source and notices. See:

 - [third-party notices](THIRD_PARTY_NOTICES.md)
 - [source record](SOURCE.md)
@@ -317,19 +349,18 @@ The auditable list is in
 - Metadata removal is best effort, not an anonymity guarantee.
 - Browser preview supports fewer combinations than FFmpeg.
 - MT depends on isolation; ST can still hit memory/time limits.
- Opus output is release-gated for the pinned core.
+- Opus enablement is supported by Chromium ST/MT fixture evidence, not a
+  cross-browser or arbitrary-input guarantee.
 - Projects do not contain source bytes by default and require reattachment.
 - Cross-browser/mobile and exhaustive MT performance matrices remain
  unrecorded; published support claims must stay within the tested evidence.

 ## Roadmap

-1. Complete Quick Convert and structural-export browser verification with the
-   real pinned ST/MT cores, including fallback and queued execution.
-2. Verify waveform, loudness normalization and combined filters in browsers.
-3. Verify metadata/chapter/subtitle round trips in browsers.
-4. Verify bounded thumbnails/contact sheets, projects, derivative-cache reuse
-   and export in browsers.
-5. Complete accessibility, mobile, performance and nested Portal matrices.
-6. Commit/tag exact source, publish its reviewed Corresponding Source, assemble
-   the exact production ZIP through Portal and verify deployed headers.
+1. Extend the evidence matrix beyond Chromium to Firefox, Safari and mobile;
+   broaden MT operation parity and replace the one-run performance observation
+   with repeated cold/warm measurements.
+2. Evaluate optional editing breadth without weakening local-first guarantees:
+   additional reviewed transition shapes, richer scene-ranking controls and
+   explicit transition audio-curve choices beyond the current bounded uniform
+   crossfade.
--- a/SOURCE.md
+++ b/SOURCE.md
@@ -1,6 +1,6 @@
 # Source and reproducibility record

-This file identifies the source corresponding to av-tools 0.1.0. It is not a
+This file identifies the source corresponding to av-tools 0.2.0. It is not a
 substitute for satisfying a component's licence or for delivering complete
 Corresponding Source with an object-code release.

@@ -9,9 +9,9 @@ Corresponding Source with an object-code release.
 - Canonical repository:
  `git@git.add-ideas.de:zemion/av-tools.git`
 - Browser source: `https://git.add-ideas.de/zemion/av-tools`
- Version: `0.1.0`
- Release source identity: immutable annotated tag `v0.1.0`
-  (`refs/tags/v0.1.0`) in the canonical repository.
+- Version: `0.2.0`
+- Release source identity: immutable annotated tag `v0.2.0`
+  (`refs/tags/v0.2.0`) in the canonical repository.
 - Application licence: `GPL-3.0-or-later`; full GPL version 3 terms in
  `LICENSE`.
 - Copyright: Copyright © 2026 Albrecht Degering.
@@ -22,10 +22,10 @@ the tag exists, is annotated, points to the reviewed release commit and is
 available without authentication:

 ```sh
-test "$(git cat-file -t v0.1.0)" = tag
-git rev-parse v0.1.0^{commit}
+test "$(git cat-file -t v0.2.0)" = tag
+git rev-parse v0.2.0^{commit}
 git ls-remote --tags \
-  https://git.add-ideas.de/zemion/av-tools.git refs/tags/v0.1.0
+  https://git.add-ideas.de/zemion/av-tools.git refs/tags/v0.2.0
 ```

 The Toolbox manifest names the canonical repository and SPDX licence. Publish
@@ -40,34 +40,66 @@ the tag/source archive beside the binary release and checksum.
 | `@ffmpeg/ffmpeg`             | 0.12.15       | `sha512-1C8Obr4GsN3xw+/1Ww6PFM84wSQAGsdoTuTWPOj2OizsRDLT4CXTaVjPhkw6ARyDus1B9X/L2LiXHqYYsGnRFw==` |
 | `@ffmpeg/util`               | 0.12.2        | `sha512-ouyoW+4JB7WxjeZ2y6KpRvB+dLp7Cp4ro8z0HIVpZVCM7AwFlHa0c4R8Y/a4M3wMqATpYKhC7lSFHQ0T11MEDw==` |
 | `@ffmpeg/types` (transitive) | 0.12.4        | `sha512-k9vJQNBGTxE5AhYDtOYR5rO5fKsspbg51gbcwtbkw2lCdoIILzklulcjJfIDwrtn7XhDeF2M+THwJ2FGrLeV6A==` |
-| `@ffmpeg/core`               | 0.12.10       | `sha512-dzNplnn2Nxle2c2i2rrDhqcB19q9cglCkWnoMTDN9Q9l3PvdjZWd1HfSPjCNWc/p8Q3CT+Es9fWOR0UhAeYQZA==` |
-| `@ffmpeg/core-mt`            | 0.12.10       | `sha512-atyRTOpa58bLCIgd6GXBZAXWyWD3AUoQyzxqjvGhp9MuSzdILtOTI62ffLswBsCnLq15lQ8IETHUpm1oe4V9FQ==` |

-Install exact packages and recreate the copied same-origin assets without a
+Install exact packages and recreate the verified same-origin assets without a
 network fetch during the production build:

 ```sh
 npm ci
 npm run vendor:ffmpeg
-npm run vendor:verify
+npm run vendor:verify-runtime
 npm run build
 ```

-`scripts/copy-ffmpeg-assets.mjs` copies the ESM distributions from the
-installed core packages; it does not download them. The copied bytes are:
+`scripts/copy-ffmpeg-assets.mjs` fails closed against
+`scripts/reviewed-ffmpeg-core-lock.json`, verifies the deterministic tracked
+ZIP and unpacks only its five declared entries. It does not download them or
+fall back to published core packages. The reviewed bytes are:
+
+For a publication check, generate the build-qualified Corresponding Source
+archive and run `npm run vendor:verify`; that stricter gate hashes the archive
+as well as every runtime input.

 | Release path                                                                 |    Bytes | SHA-256                                                            |
-| ------------------------------------------------ | -------: | ------------------------------------------------------------------ |
-| `vendor/ffmpeg/0.12.10/st/ffmpeg-core.js`        |   111804 | `67a48f11645f85439f3fde4f2119042c16b374b910206b7a7a24f342e28dcae3` |
-| `vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm`      | 32232419 | `9f57947a5bd530d8f00c5b3f2cb2a3492faa7e5d823315342d6a8656d0a6b7b7` |
-| `vendor/ffmpeg/0.12.10/mt/ffmpeg-core.js`        |   128947 | `270a2e6ff945e173238610669a3f7132df5f9c52698a9bf708cf5c2ab6bda0de` |
-| `vendor/ffmpeg/0.12.10/mt/ffmpeg-core.wasm`      | 32718323 | `be2c97605366b78f3f13e21b52e81a55a79e1f29c133b03a68ec187b1a2ec41a` |
-| `vendor/ffmpeg/0.12.10/mt/ffmpeg-core.worker.js` |     2115 | `f77898d631dc010b45c29c23cb4379c611a7d7b131bf591d08a656bb729a4ca3` |
+| ---------------------------------------------------------------------------- | -------: | ------------------------------------------------------------------ |
+| `vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.js`                 |   111804 | `80c05d79d0e4e9434977b76cb851d10ddf2bfd378570178700d2c43b8afdcb24` |
+| `vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm`               | 32232580 | `fe41ddc77220cef6c04f5d48eeffcaaaef179ad270642e098f9945013aa0c9dc` |
+| `vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.js`                 |   128953 | `4f2650099ab70cb2583951c0421147c62bea6c18dfbba5cfae4d7698b5d0ab62` |
+| `vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.wasm`               | 32718455 | `abbead010cb0448b26f01a36a3c8c03a6b04aca07812ddd4719a7f4b6bf4b645` |
+| `vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.worker.js`          |     2115 | `f77898d631dc010b45c29c23cb4379c611a7d7b131bf591d08a656bb729a4ca3` |
+| `vendor/ffmpeg-core-0.12.10-reviewed-stack5m.1.zip` (deterministic artifact) | 21338974 | `ebc068c6d096de55ae3335b04b7121130665f5b0ffa7a828067122733f55185f` |
+
+## Bundled contact-sheet font
+
+Contact-sheet labels use one unmodified DejaVu Sans 2.37 TrueType file. It is
+served same-origin and mounted read-only for the duration of a labelled job;
+the browser verifies its size and SHA-256 before use.
+
+| Release path                |   Bytes | SHA-256                                                            |
+| --------------------------- | ------: | ------------------------------------------------------------------ |
+| `fonts/DejaVuSans.ttf`      | 757,076 | `7da195a74c55bef988d0d48f9508bd5d849425c1770dba5d7bfc6ce9ed848954` |
+| `LICENSES/DEJAVU_FONTS.txt` |     n/a | licence text embedded in the reviewed font and official archive    |
+
+The byte-for-byte source is `ttf/DejaVuSans.ttf` in the official
+`dejavu-fonts-ttf-2.37.tar.bz2` release:
+
+- project download record: `https://dejavu-fonts.github.io/Download.html`;
+- archive URL:
+  `https://downloads.sourceforge.net/project/dejavu/dejavu/2.37/dejavu-fonts-ttf-2.37.tar.bz2`;
+- archive SHA-256:
+  `fa9ca4d13871dd122f61258a80d01751d603b4d3ee14095d65453b4e846e17d7`;
+- corresponding upstream tag `version_2_37`, commit
+  `0eda8a319c08835009849583cd090bb5b141ce25`.
+
+The release archive and the bundled file were independently hashed and the
+font's internal version string is `Version 2.37`. The file is not modified or
+subsetted. Its Bitstream Vera/Arev permission terms are reproduced verbatim in
+`LICENSES/DEJAVU_FONTS.txt`.

 ## Corresponding ffmpeg.wasm and FFmpeg source

- Upstream ffmpeg.wasm release tag containing `@ffmpeg/ffmpeg` 0.12.15,
-  `@ffmpeg/core` 0.12.10 and `@ffmpeg/core-mt` 0.12.10:
+- Base ffmpeg.wasm release tag containing `@ffmpeg/ffmpeg` 0.12.15 and the
+  source configuration for core 0.12.10:
  `v12.15` at `71aa99d37c02a7b4c435275ca9ef50e612f6efa1`.
 - FFmpeg source selected by that revision's `Dockerfile`: tag `n5.1.4`,
  peeled Git commit `4729204c17f756e186d622060088371d10b34f7e`.
@@ -88,6 +120,14 @@ The upstream build control files are `Dockerfile`, `Makefile`,
 `build/` at the ffmpeg.wasm release revision. `make prd` builds single-thread;
 `make prd-mt` builds multithread.

+The shipped profile is rebuilt by
+`scripts/build-reviewed-ffmpeg-core.sh`. It applies upstream ffmpeg.wasm commit
+`b409e36475bc21f0451b5b1e1d126fa82871439a` (`-sSTACK_SIZE=5MB`), uses exact
+Emscripten 3.1.40 and CMake 3.27.9 identities, makes upstream container-stage
+isolation explicit and refuses maintainer-local paths in output. The exact
+source archive, toolchain, patch, asset and Opus-gate identities are locked in
+`scripts/reviewed-ffmpeg-core-lock.json`.
+
 The Dockerfile uses branch names for two inputs. Repository history resolves
 those refs to tips that predate the ffmpeg.wasm v12.15 release and have not
 changed since:
@@ -121,10 +161,13 @@ npm run source:package
 ```

 The command writes
-`release/ffmpeg-core-0.12.10-corresponding-source.tar.xz` and its
+`release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz`
+and its
 `.sha256` sidecar. Pass `-- --force` only to replace those exact outputs.
-The npm packages contain the resulting binaries but not every linked
-component's source and legal file, so publish this reviewed bundle and the
+The reviewed archive for this build profile is 43,050,052 bytes with SHA-256
+`2ab505f72be883d1257bc71cbb93880d1ade5bc029792621cb87b4ecc068399a`.
+The reviewed object-code archive does not contain every linked component's
+source and legal file, so publish this Corresponding Source bundle and the
 notices beside the object code. A homepage link alone is not asserted to
 satisfy GPL source obligations.

--- a/THIRD_PARTY_NOTICES.md
+++ b/THIRD_PARTY_NOTICES.md
@@ -1,6 +1,6 @@
 # Third-party notices

-av-tools 0.1.0 is Copyright © 2026 Albrecht Degering and licensed
+av-tools 0.2.0 is Copyright © 2026 Albrecht Degering and licensed
 GPL-3.0-or-later; see the root `LICENSE`. This inventory describes third-party
 inputs. It is informational, not legal advice, and does not replace their
 terms. Files under `LICENSES/` reproduce available terms. A packaged ZIP also
@@ -10,29 +10,32 @@ receives licence files shipped by installed runtime npm packages under
 ## Browser runtime

 | Package                          | Version                    | Licence declared upstream | Project source                                | Role                                                    | Distribution                                              |
-| -------------------------------- | ------- | ------------------------- | --------------------------------------------- | ------------------------------------------------------------- | -------------------------------------- |
+| -------------------------------- | -------------------------- | ------------------------- | --------------------------------------------- | ------------------------------------------------------- | --------------------------------------------------------- |
 | `@add-ideas/toolbox-contract`    | 0.2.2                      | Apache-2.0                | `https://git.add-ideas.de/zemion/toolbox-sdk` | typed manifest/context contract                         | shipped, bundled                                          |
 | `@add-ideas/toolbox-shell-react` | 0.2.2                      | Apache-2.0                | `https://git.add-ideas.de/zemion/toolbox-sdk` | shared Toolbox application shell                        | shipped, bundled                                          |
 | `@ffmpeg/ffmpeg`                 | 0.12.15                    | MIT                       | `https://github.com/ffmpegwasm/ffmpeg.wasm`   | browser worker and high-level FFmpeg API                | shipped, bundled                                          |
 | `@ffmpeg/util`                   | 0.12.2                     | MIT                       | `https://github.com/ffmpegwasm/ffmpeg.wasm`   | byte/blob helpers                                       | shipped, bundled                                          |
 | `@ffmpeg/types`                  | 0.12.4                     | MIT                       | `https://github.com/ffmpegwasm/ffmpeg.wasm`   | transitive runtime API types                            | shipped as compiled/bundled references                    |
-| `@ffmpeg/core`                   | 0.12.10 | GPL-2.0-or-later package  | `https://github.com/ffmpegwasm/ffmpeg.wasm`   | single-thread FFmpeg JavaScript and WebAssembly               | shipped verbatim as self-hosted assets |
-| `@ffmpeg/core-mt`                | 0.12.10 | GPL-2.0-or-later package  | `https://github.com/ffmpegwasm/ffmpeg.wasm`   | multithread FFmpeg JavaScript, WebAssembly and pthread worker | shipped verbatim as self-hosted assets |
+| reviewed FFmpeg WASM cores       | 0.12.10-reviewed-stack5m.1 | GPL-enabled combined work | `https://github.com/ffmpegwasm/ffmpeg.wasm`   | ST/MT FFmpeg JavaScript, WebAssembly and pthread worker | rebuilt from locked source and shipped as verified assets |
 | `fflate`                         | 0.8.3                      | MIT                       | `https://github.com/101arrowz/fflate`         | in-browser ZIP creation                                 | shipped, bundled                                          |
+| DejaVu Sans                      | 2.37                       | Bitstream Vera/Arev terms | `https://dejavu-fonts.github.io/`             | deterministic local contact-sheet labels                | shipped unmodified as reviewed TTF                        |
 | `react`                          | 19.2.7                     | MIT                       | `https://github.com/facebook/react`           | user-interface runtime                                  | shipped, bundled                                          |
 | `react-dom`                      | 19.2.7                     | MIT                       | `https://github.com/facebook/react`           | browser rendering                                       | shipped, bundled                                          |
 | `scheduler`                      | 0.27.0                     | MIT                       | `https://github.com/facebook/react`           | transitive React scheduling runtime                     | shipped, bundled                                          |

 The MIT text inspected in the ffmpeg.wasm source is
-`LICENSES/ffmpeg.wasm-MIT.txt`. The core npm tarballs do not contain a licence
-file, but their package manifests declare `GPL-2.0-or-later`;
-`LICENSES/GPL-2.0-or-later.txt` reproduces GPL version 2. These notices do not
-make the complete application “MIT-only.”
+`LICENSES/ffmpeg.wasm-MIT.txt`. The reviewed cores enable GPL FFmpeg features
+and statically link GPL components; `LICENSES/GPL-2.0-or-later.txt` reproduces
+GPL version 2. These notices do not make the complete application “MIT-only.”
+
+The reviewed DejaVu file is identified byte-for-byte in `SOURCE.md`; its full
+embedded terms are in `LICENSES/DEJAVU_FONTS.txt`. No remote or system font is
+used as a runtime fallback.

 ## Native components linked into the WebAssembly cores

 The following list is derived from the `v12.15` ffmpeg.wasm Dockerfile, the
-configuration embedded in the copied 0.12.10 WASM and the resolved histories
+configuration embedded in the reviewed 0.12.10 WASM and the resolved histories
 of its source repositories. Branch-based inputs are recorded below as exact
 commits. The combined core is GPL-enabled. Individual projects retain their
 own terms, notices, patent considerations and corresponding-source
--- a/deployment/caddy.example
+++ b/deployment/caddy.example
@@ -14,7 +14,7 @@ tools.example.test {
 	@wasm path_regexp wasm \.wasm$
 	header @wasm Content-Type "application/wasm"

-	@immutable path_regexp immutable ^/av/(?:vendor/ffmpeg/0\.12\.10/(?:st|mt)/ffmpeg-core(?:\.worker)?\.(?:js|wasm)|assets/.*-[A-Za-z0-9_-]{8,}\.[^/]+)$
+	@immutable path_regexp immutable ^/av/(?:vendor/ffmpeg/0\.12\.10-reviewed-stack5m\.1/(?:st|mt)/ffmpeg-core(?:\.worker)?\.(?:js|wasm)|assets/.*-[A-Za-z0-9_-]{8,}\.[^/]+)$
 	header @immutable Cache-Control "public, max-age=31536000, immutable"

 	redir /av /av/ 308
--- a/deployment/headers.md
+++ b/deployment/headers.md
@@ -32,7 +32,7 @@ cross-origin resource policy and is outside the supported deployment profile.

 Use `no-cache` for `index.html`, `toolbox-app.json`, notices and other stable
 names. The files under the exact version directory
-`vendor/ffmpeg/0.12.10/{st,mt}/` are content-verified and may use:
+`vendor/ffmpeg/0.12.10-reviewed-stack5m.1/{st,mt}/` are content-verified and may use:

 ```text
 Cache-Control: public, max-age=31536000, immutable
@@ -55,7 +55,7 @@ For a host with a `_headers`-style configuration, adapt:
  Content-Security-Policy: default-src 'self'; script-src 'self' 'wasm-unsafe-eval'; worker-src 'self' blob:; connect-src 'self'; img-src 'self' blob: data:; media-src 'self' blob:; font-src 'self'; style-src 'self'; object-src 'none'; frame-src 'none'; frame-ancestors 'none'; base-uri 'none'; form-action 'none'
  Cache-Control: no-cache

-/av/vendor/ffmpeg/0.12.10/*
+/av/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/*
  Cache-Control: public, max-age=31536000, immutable

 /av/assets/*
@@ -68,7 +68,7 @@ real response rather than relying only on configuration:

 ```sh
 curl -sSI https://tools.example.test/av/ | sed -n '1,30p'
-curl -sSI https://tools.example.test/av/vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm | sed -n '1,30p'
+curl -sSI https://tools.example.test/av/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm | sed -n '1,30p'
 ```

 In browser developer tools, also verify `window.crossOriginIsolated === true`,
--- a/deployment/nginx.example.conf
+++ b/deployment/nginx.example.conf
@@ -3,7 +3,7 @@

 map $uri $av_tools_cache_control {
  default "no-cache";
-  "~^/(?:.*/)?vendor/ffmpeg/0\.12\.10/(?:st|mt)/ffmpeg-core(?:\.worker)?\.(?:js|wasm)$" "public, max-age=31536000, immutable";
+  "~^/(?:.*/)?vendor/ffmpeg/0\.12\.10-reviewed-stack5m\.1/(?:st|mt)/ffmpeg-core(?:\.worker)?\.(?:js|wasm)$" "public, max-age=31536000, immutable";
  "~^/(?:.*/)?assets/.*-[A-Za-z0-9_-]{8,}\.[^/]+$" "public, max-age=31536000, immutable";
 }

--- a/docs/FFMPEG_BUILD.md
+++ b/docs/FFMPEG_BUILD.md
@@ -1,13 +1,13 @@
 # FFmpeg WebAssembly build record

-av-tools ships the published ESM assets from `@ffmpeg/core` and
-`@ffmpeg/core-mt` **0.12.10**. The browser wrapper is `@ffmpeg/ffmpeg`
-**0.12.15** and helpers are `@ffmpeg/util` **0.12.2**. All versions are exact,
-not ranges.
+av-tools ships the locally rebuilt, reviewed core profile
+`0.12.10-reviewed-stack5m.1` in single-thread and multithread forms. The
+browser wrapper is `@ffmpeg/ffmpeg` **0.12.15** and helpers are
+`@ffmpeg/util` **0.12.2**. All versions and build inputs are exact, not ranges.

 ## Underlying build

-The matching ffmpeg.wasm upstream release is `v12.15` at
+The base ffmpeg.wasm upstream release is `v12.15` at
 `71aa99d37c02a7b4c435275ca9ef50e612f6efa1`. Its Dockerfile selects:

 - FFmpeg **n5.1.4** (libavcodec 59.37.100);
@@ -15,6 +15,14 @@ The matching ffmpeg.wasm upstream release is `v12.15` at
 - production `-O3 -msimd128`;
 - pthread flags for the MT build and explicit thread disabling for ST.

+The reviewed profile then applies upstream ffmpeg.wasm commit
+`b409e36475bc21f0451b5b1e1d126fa82871439a` to select a 5 MiB Emscripten stack.
+That upstream fix addresses the libopus zero-byte/out-of-bounds failures
+reported in issues `#591` and `#775`. The local driver additionally makes the
+upstream container-stage dependency isolation explicit, disables native x265
+assembly for the wasm32 build, bounds parallel jobs and refuses output that
+contains the maintainer's repository or SDK paths.
+
 The build configuration embedded in both copied WASM files is:

 ```text
@@ -35,8 +43,8 @@ The build configuration embedded in both copied WASM files is:
 --cxx=em++
 --objcc=emcc
 --dep-cc=emcc
--extra-cflags='-I/opt/include -O3 -msimd128'
--extra-cxxflags='-I/opt/include -O3 -msimd128'
+--extra-cflags='-I../../../../install/include -O3 -msimd128'
+--extra-cxxflags='-I../../../../install/include -O3 -msimd128'
 --enable-gpl
 --enable-libx264
 --enable-libx265
@@ -76,16 +84,26 @@ respective branch tips. `SOURCE.md` records retrieval commands.

 | Mode | File                       |    Bytes | SHA-256                                                            |
 | ---- | -------------------------- | -------: | ------------------------------------------------------------------ |
-| ST   | `st/ffmpeg-core.js`        |   111804 | `67a48f11645f85439f3fde4f2119042c16b374b910206b7a7a24f342e28dcae3` |
-| ST   | `st/ffmpeg-core.wasm`      | 32232419 | `9f57947a5bd530d8f00c5b3f2cb2a3492faa7e5d823315342d6a8656d0a6b7b7` |
-| MT   | `mt/ffmpeg-core.js`        |   128947 | `270a2e6ff945e173238610669a3f7132df5f9c52698a9bf708cf5c2ab6bda0de` |
-| MT   | `mt/ffmpeg-core.wasm`      | 32718323 | `be2c97605366b78f3f13e21b52e81a55a79e1f29c133b03a68ec187b1a2ec41a` |
+| ST   | `st/ffmpeg-core.js`        |   111804 | `80c05d79d0e4e9434977b76cb851d10ddf2bfd378570178700d2c43b8afdcb24` |
+| ST   | `st/ffmpeg-core.wasm`      | 32232580 | `fe41ddc77220cef6c04f5d48eeffcaaaef179ad270642e098f9945013aa0c9dc` |
+| MT   | `mt/ffmpeg-core.js`        |   128953 | `4f2650099ab70cb2583951c0421147c62bea6c18dfbba5cfae4d7698b5d0ab62` |
+| MT   | `mt/ffmpeg-core.wasm`      | 32718455 | `abbead010cb0448b26f01a36a3c8c03a6b04aca07812ddd4719a7f4b6bf4b645` |
 | MT   | `mt/ffmpeg-core.worker.js` |     2115 | `f77898d631dc010b45c29c23cb4379c611a7d7b131bf591d08a656bb729a4ca3` |

-`npm run vendor:ffmpeg` copies these files from `node_modules` to
-`public/vendor/ffmpeg/0.12.10/`; `npm run vendor:verify` checks versions,
-sizes, paths and digests. Vite then copies them unchanged into `dist`. A normal
-production build performs no network download.
+The deterministic five-file repository artifact is 21,338,974 bytes with
+SHA-256
+`ebc068c6d096de55ae3335b04b7121130665f5b0ffa7a828067122733f55185f`.
+
+`npm run vendor:ffmpeg` verifies and unpacks the deterministic tracked core
+artifact to
+`public/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/`;
+`npm run vendor:verify-runtime` checks the build profile,
+source/toolchain/patch identity, tracked artifact, generated paths, sizes and
+digests without requiring a release-directory download. The stricter
+`npm run vendor:verify` release gate also hashes the build-qualified
+Corresponding Source archive. Vite then copies the verified bytes into `dist`.
+A normal production build performs no network download and cannot fall back
+to the older published npm core bytes.

 ## Multithread Chromium guardrail

@@ -118,26 +136,42 @@ This is a conservative browser-memory guardrail, not a guarantee that sixteen
 large jobs or three large contact sheets fit in memory. Cancellation and
 failed filesystem-cleanup recovery continue to recreate the core immediately.

-## Opus regression risk
+## Opus regression evidence

-Pinned core 0.12.10 predates upstream ffmpeg.wasm fixes associated with stack
-size and Opus zero-byte/out-of-bounds failures (including upstream issues
-`#591` and `#775`). Therefore:
+Published core 0.12.10 predates the upstream stack-size fix and stalled in the
+real Opus preset path even though it advertised the `opus` muxer and
+`libopus` encoder. Capability discovery alone was therefore not accepted as
+enablement evidence.

- decoder/encoder listing is not enough to certify Opus;
- real ST and MT fixture encodes must produce a non-empty, re-probeable output;
- the Opus audio and VP9/Opus presets must remain disabled with a diagnostic
-  if that smoke fails;
- a core upgrade requires new checksums, capability snapshots, legal review
-  and regression tests.
+On 2026-07-26 the Chromium harness used the checked
+`tests/fixtures/generated/tone.wav` fixture (32,102 bytes, SHA-256
+`0fd1f54d6be2f1cc7fd778775dd29cf184770d3716cf3394bf03ed54ac264c3c`)
+and the real built-in `audio-opus` preset/command planner. After rebuilding
+with the reviewed stack profile, the isolated ST and MT runs each:

-This is a known pinned-core risk, not a claim that every Opus job fails.
+- loaded the requested mode rather than a fallback;
+- mapped PCM audio to `opus (libopus)`;
+- opened the declared Opus output and reported its libopus encoder;
+- returned non-empty bytes within its independent containment limit;
+- re-probed the result as positive-duration Opus audio.
+
+```sh
+# Record JSON evidence.
+npm run evidence:opus
+
+# Positive Opus enablement/release gate.
+npm run test:opus-regression
+```
+
+The Opus audio and VP9/Opus presets are enabled only when the reviewed-core
+lock records both passing modes and runtime discovery finds every preset
+requirement. This is exact Chromium fixture evidence, not a claim about every
+browser, input or possible Opus build.

 ## Licence consequence

-The core packages declare GPL-2.0-or-later and the actual build enables GPL and
-links external codecs. The wrapper/util are MIT. av-tools is
-GPL-3.0-or-later, and the distributed application must not be described as
-MIT-only. Publish the reviewed Corresponding Source and external notices with
-the binary release. See `LICENSE`, `LICENSES/`, `THIRD_PARTY_NOTICES.md` and
-`SOURCE.md`.
+The actual core build enables GPL and links external codecs. The wrapper/util
+are MIT. av-tools is GPL-3.0-or-later, and the distributed application must
+not be described as MIT-only. Publish the reviewed Corresponding Source and
+external notices with the binary release. See `LICENSE`, `LICENSES/`,
+`THIRD_PARTY_NOTICES.md` and `SOURCE.md`.
--- a/docs/FORMAT_SUPPORT.md
+++ b/docs/FORMAT_SUPPORT.md
@@ -5,7 +5,7 @@ extensions or this document. The app queries muxers, demuxers, decoders,
 encoders and filters; a preset is disabled with missing components listed.
 Browser playback is a separate capability checked with MIME/media APIs.

-## 0.1.0 candidate fixture matrix
+## 0.2.0 release fixture matrix

 All 15 files are generated and re-probed with native FFmpeg 7.1.3 for test
 preparation and pass the checksum/probe verifier. That proves fixture
@@ -42,9 +42,9 @@ browser may still be unable to preview the result.
 Preset availability always depends on detected runtime requirements:

 | Preset family      | Required examples                        | Browser result preview                                   |
-| ------------------ | ---------------------------------------- | ------------------------------------------------------ |
+| ------------------ | ---------------------------------------- | -------------------------------------------------------- |
 | MP4 H.264/AAC      | `mp4`, `libx264`, `aac`                  | usually, but verify actual output                        |
-| WebM VP9/Opus      | `webm`, `libvpx-vp9`, `libopus`          | browser-dependent; Opus core regression gate applies   |
+| WebM VP9/Opus      | `webm`, `libvpx-vp9`, `libopus`          | enabled when the loaded core advertises all requirements |
 | WebM VP8/Vorbis    | `webm`, `libvpx`, `libvorbis`            | commonly Chromium/Firefox                                |
 | Matroska H.264/AAC | `matroska`, `libx264`, `aac`             | generally download-only in browsers                      |
 | animated WebP      | `webp`, `libwebp_anim`                   | browser-dependent image preview                          |
@@ -52,7 +52,7 @@ Preset availability always depends on detected runtime requirements:
 | MP3                | `mp3`, `libmp3lame`                      | commonly playable                                        |
 | M4A/AAC            | `ipod`, `aac`                            | commonly playable                                        |
 | Ogg Vorbis         | `ogg`, `libvorbis`                       | browser-dependent                                        |
-| Opus               | `opus`, `libopus`                        | browser-dependent; pinned-core regression gate applies |
+| Opus               | `opus`, `libopus`                        | Chromium ST/MT encode and re-probe recorded              |
 | WAV/PCM            | `wav`, `pcm_s16le`                       | commonly playable                                        |
 | FLAC               | `flac`, `flac`                           | browser-dependent                                        |

@@ -77,11 +77,30 @@ remux avoids re-encoding compatible streams but may change container metadata.
 - Normalized concat uses an explicit export preset and requires an explicit
  insert-silence, drop-all-audio or reject policy when clips have mismatched
  audio presence.
+- Normalized concat can overlap every edit with one uniform 0.04–10 second
+  `xfade` and, when audio is retained, `acrossfade`. End clips must contain at
+  least one transition duration and internal clips two; the active core must
+  expose each required filter.
 - Crop, resize, frame-rate conversion, fades, normalization, burn-in and
  contact sheets require specific filters discovered at runtime.
 - Even-dimension correction is applied when the selected pixel format/encoder
  requires it and is reported in the plan/result.

+## Images and scene selection
+
+Thumbnail/contact-sheet scene mode first performs a bounded full-source
+analysis with `select`/`showinfo`, stopping after at most 100 qualifying
+frames. Extraction then selects those exact source PTS values; no guessed time
+rounding or remote analysis is used. If no frame meets the 0.01–0.95 threshold,
+the operation reports that result and asks for a lower threshold or a
+deterministic selection mode.
+
+Contact-sheet labels require runtime `drawtext`. The app mounts only its
+same-origin DejaVu Sans 2.37 asset after verifying 757,076 bytes and SHA-256
+`7da195a74c55bef988d0d48f9508bd5d849425c1770dba5d7bfc6ce9ed848954`.
+No remote or host-system font fallback is used. `SOURCE.md` and
+`LICENSES/DEJAVU_FONTS.txt` provide provenance and terms.
+
 ## Subtitles

 The text fixtures cover SRT, WebVTT and ASS import with explicit time shift.
@@ -115,8 +134,9 @@ elements do not reliably expose them, so ffprobe round-trip is authoritative.
 - frame-accurate stream-copy trimming;
 - complete metadata erasure/anonymity;
 - browser preview of every FFmpeg-readable result;
- Opus presets until real non-empty ST/MT encoding smoke passes for core
-  0.12.10;
+- Opus on browsers, inputs or deployments outside the exact reviewed
+  Chromium regression: both ST and MT pass the non-empty encode/re-probe gate,
+  but runtime capability discovery and normal per-job limits still apply;
 - any capability omitted by the active core's runtime query.

 Update this file only from re-probed generated/public-domain fixtures and
--- a/docs/KNOWN_LIMITATIONS.md
+++ b/docs/KNOWN_LIMITATIONS.md
@@ -1,6 +1,6 @@
 # Known limitations

-This is the conservative 0.1.0 development baseline. A capability appearing in
+This is the conservative 0.2.0 release baseline. A capability appearing in
 FFmpeg output does not remove these product/browser/resource limits.

 ## Functional
@@ -13,6 +13,9 @@ FFmpeg output does not remove these product/browser/resource limits.
  frame-accurate. Accurate mode requires decoding/re-encoding.
 - Stream-copy concatenate works only when selected streams and codec/container
  parameters are compatible. Other input needs normalized re-encoding.
+- Crossfades are uniform fade/triangular-curve transitions on normalized
+  sequential joins, not arbitrary transition effects or overlapping timeline
+  tracks. They require enough material on both sides of every internal edit.
 - Re-encoding is not lossless. PCM/FLAC can preserve decoded audio samples but
  cannot restore information already lost in a source.
 - Metadata removal is best effort. Muxers may add structural/encoder fields,
@@ -26,6 +29,12 @@ FFmpeg output does not remove these product/browser/resource limits.
  page discards queued work.
 - A file-generating batch and its managed result collection are bounded to 255
  outputs, leaving the 256th ZIP entry available for an optional export report.
+- Scene analysis scans the source until it finds the requested changes or
+  reaches the end, retains at most 100 exact PTS results and can therefore take
+  about as long as a full decode. It does not begin an export implicitly when
+  no frame meets the chosen threshold.
+- Labelled contact sheets require a core with `drawtext`; the reviewed local
+  font does not make that filter available on a core that omits it.
 - Preview proxies are bounded, lossy H.264/AAC derivatives for local playback;
  they do not replace the source or guarantee that every browser can play the
  result.
@@ -38,8 +47,9 @@ FFmpeg output does not remove these product/browser/resource limits.
  support fewer container/codec combinations.
 - Browser support, codec policy and memory differ across Chromium, Firefox and
  Safari and across desktop/mobile versions.
- Core 0.12.10 has an Opus regression risk. Opus remains release-gated until
-  non-empty, re-probeable ST and MT fixture outputs pass.
+- The reviewed 0.12.10 core profile passes the non-empty Opus encode/re-probe
+  gate in isolated Chromium ST and MT runs. That evidence is not a
+  cross-browser or every-input Opus guarantee.
 - MT needs HTTPS, COOP/COEP/CORP and `SharedArrayBuffer`. ST fallback works
  without isolation but is not a guarantee that a large job fits.
 - Top-level navigation is supported; iframe embedding is not.
@@ -69,7 +79,7 @@ FFmpeg output does not remove these product/browser/resource limits.
  verification against the live container.
 - The application is GPL-3.0-or-later and its native legal files and pinned
  source identities are included in the release record. Publish the production
-  ZIP/checksum, exact `v0.1.0` source and FFmpeg Corresponding Source bundle
+  ZIP/checksum, exact `v0.2.0` source and FFmpeg Corresponding Source bundle
  together; development-only smoke artifacts must not be distributed.
 - Chromium covers a broad real pinned-core ST operation matrix, a real MT
  H.264/AAC conversion, MT-to-ST fallback, nested static/Toolbox-context
--- a/docs/PERFORMANCE.md
+++ b/docs/PERFORMANCE.md
@@ -6,12 +6,13 @@ output at once. No hardware encoder is used.

 ## Fixed download footprint

-Uncompressed self-hosted core assets for 0.12.10:
+Uncompressed self-hosted core assets for
+`0.12.10-reviewed-stack5m.1`:

 | Mode          |   JavaScript/worker |         WASM |        Total |
 | ------------- | ------------------: | -----------: | -----------: |
-| single-thread |           111,804 B | 32,232,419 B | 32,344,223 B |
-| multithread   | 128,947 B + 2,115 B | 32,718,323 B | 32,849,385 B |
+| single-thread |           111,804 B | 32,232,580 B | 32,344,384 B |
+| multithread   | 128,953 B + 2,115 B | 32,718,455 B | 32,849,523 B |

 Only the selected mode is loaded. HTTP compression may reduce JavaScript
 transfer but not necessarily WASM to the same degree; report transfer and
@@ -72,9 +73,18 @@ Estimated output warns at 512 MiB and is blocked at 1 GiB. FFmpeg jobs are
 serial; the application retains at most eight scheduled operations in its
 in-memory queue. Timeline clips are capped at 100, streams per input at 64,
 images at 8192×8192/67,108,864 pixels, generated output files at 255,
-contact-sheet cells at 500 and runtime at four hours. The documented
-ffmpeg.wasm input ceiling is 2 GiB, but real limits can be substantially lower
-on mobile or memory-constrained browsers.
+contact-sheet cells at 500, scene-change results at 100, crossfades at 10
+seconds and runtime at four hours. Scene selection is a bounded two-step
+workflow but its analysis step can still decode the complete source when few
+frames meet the threshold. The documented ffmpeg.wasm input ceiling is 2 GiB,
+but real limits can be substantially lower on mobile or memory-constrained
+browsers.
+
+Source inspection has a bounded, size-aware watchdog: 30 seconds for small
+files, a two-MiB-per-second scan budget for larger files, and a five-minute
+ceiling. Recognized local audio/video can begin browser playback from its
+temporary object URL while that worker inspection continues; completed probe
+metadata remains authoritative for editing and export.

 Lowering resolution, duration, frame rate, passes and output count reduces
 work. MT can be faster but consumes more memory/CPU and requires isolation; ST
--- a/docs/PORTAL_REQUIREMENTS.md
+++ b/docs/PORTAL_REQUIREMENTS.md
@@ -18,7 +18,7 @@ X-Content-Type-Options: nosniff

 Serve `.wasm` as `application/wasm`, JavaScript modules as a JavaScript MIME
 type and JSON as `application/json`. Test real responses under
-`/apps/av/vendor/ffmpeg/0.12.10/...`; a file-extension allowlist alone does not
+`/apps/av/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/...`; a file-extension allowlist alone does not
 prove the MIME type.

 Suggested CSP:
@@ -43,45 +43,36 @@ form-action 'none';
 `'unsafe-eval'` is unnecessary. `worker-src blob:` covers the wrapper-created
 worker path. `media-src blob:` permits local source/result previews.

-## Immutable reference and active-worktree state
+## Reviewed Portal state

-Portal revision `bda9da044d61c109afd9969d357cc27f76648938` already sends COOP
-`same-origin`, COEP `require-corp`, CORP `same-origin`, `script-src 'self'
-'wasm-unsafe-eval'`, and `worker-src 'self' blob:`. Its packaged nginx CSP does
-**not** declare `media-src`; `default-src 'self'` therefore blocks local
-`blob:` audio/video URLs. The expected browser diagnostic is equivalent to:
+Portal revision `5c052bc6d1073a66600cfddc44c0e16da34bede8` (tag `v0.6.0`)
+already sends COOP `same-origin`, COEP `require-corp`, CORP `same-origin`,
+`script-src 'self' 'wasm-unsafe-eval'`, `worker-src 'self' blob:` and
+`media-src 'self' blob:`. Its nginx profile also maps `.wasm` explicitly to
+`application/wasm`. Local source and result Blob previews therefore require no
+CSP exception beyond that reviewed narrow media directive.

-```text
-Refused to load media from 'blob:…' because it violates
-"default-src 'self'".
-```
+As inspected on 2026-07-26, the active
+`/mnt/DATA/git/toolbox-portal/deploy/nginx.conf` has an additional worktree
+patch that extends the immutable FFmpeg cache rule from plain semantic versions
+to the one exact reviewed build profile
+`0.12.10-reviewed-stack5m.1`. The corresponding deployment tests accept the
+five reviewed core files and `version.json` while rejecting mutable-looking
+suffixes, malformed versions and unexpected paths. A clean temporary clone
+containing that exact patch passed the AV release assembly smoke without a
+known-header-gap override.

-Smallest required Portal change: append exactly
-`media-src 'self' blob:;` to that CSP. This permits only same-origin and
-in-memory Blob media; it does not permit remote media hosts, inline script or
-eval. If the Portal is not changed, conversion/download can remain available
-but Blob source/result preview must show a clear disabled reason.
-
-As inspected on 2026-07-24, the active
-`/mnt/DATA/git/toolbox-portal/deploy/nginx.conf` contains that exact directive
-as a local worktree patch. The worktree still resolves to the immutable
-revision above, so the patch is useful for local deployment testing but is not
-a committed Portal revision and must not be cited as published release
-evidence. The clean-reference assembly smoke therefore continues to require
-`--allow-known-header-gap` until a reviewed Portal commit contains the fix.
-
-The nginx profile includes `.wasm` in its static allowlist/gzip types but
-relies on the base image `mime.types`. Verify `Content-Type:
-application/wasm` against the pinned image; add an explicit mapping if the
-response differs.
+Until the cache extension is committed, cite it only as staged integration
+evidence, not as a published Portal revision. The clean `v0.6.0` rule leaves
+the reviewed profile at `no-cache`; that affects performance, not loading,
+MIME type, isolation or preview correctness.

 ## Caching

-The immutable Portal reference's cache map makes Vite content-hashed assets
-immutable but leaves versioned FFmpeg cores at `no-cache`. Correctness is
-unaffected.
-For performance, the exact directory
-`apps/av/vendor/ffmpeg/0.12.10/{st,mt}/` may receive:
+The staged Portal cache map makes Vite content-hashed assets, plain semantic
+versions and the explicitly reviewed profile immutable. For performance, the
+exact directory
+`apps/av/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/{st,mt}/` may receive:

 ```text
 Cache-Control: public, max-age=31536000, immutable
--- a/docs/REFERENCE_IMPLEMENTATIONS.md
+++ b/docs/REFERENCE_IMPLEMENTATIONS.md
@@ -1,28 +1,31 @@
 # Reference implementations

-Inspection date: **2026-07-24**.
+Inspection dates: **2026-07-24** (initial implementation) and
+**2026-07-26** (remaining-slice integration).

 The references were cloned beside av-tools under
 `/mnt/DATA/git/references/`; no reference repository was nested in this
 working tree. Revisions are full immutable commit ids.

 | Repository                                                           | Revision inspected                                                                                                     | Used for                                                                                                                                | Copied or adapted                                                                                                                                                                                                |
-| -------------------------------------------------------------------- | ----------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| -------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | av-tools, `git@git.add-ideas.de:zemion/av-tools.git`                 | no revision: canonical `main` was unborn and had no commits                                                            | canonical destination and licence/history check                                                                                         | the empty repository was scaffolded in place; no prior code existed                                                                                                                                              |
 | Toolbox SDK, `https://git.add-ideas.de/zemion/toolbox-sdk.git`       | `53c40a61ba1581246f65773fcbb1c1cfd31ac98e` (SDK 0.2.2)                                                                 | manifest schema/definition, `AppShell`, context behavior, shared styles, token-free registry, nested-path checks and toolchain baseline | published 0.2.2 packages are direct dependencies; documented usage patterns were followed; no SDK source file was copied                                                                                         |
-| Toolbox Portal, `https://git.add-ideas.de/zemion/toolbox-portal.git` | `bda9da044d61c109afd9969d357cc27f76648938`                  | release ZIP/sidecar/lock formats, independent assembly, catalogue behavior, path security, nested deployment and production headers     | no portal application source was copied; the documented artifact contract informed an independent release packager and smoke harness                     |
-| ffmpeg.wasm, `https://github.com/ffmpegwasm/ffmpeg.wasm.git`         | `f876f907c7e9b9bf51d4ed0b913a855a63ae63fc`                  | current API, worker lifecycle, filesystem, loading, ST/MT behavior, licence documentation and build layout                              | no reference-worktree code was copied; exact published npm packages are dependencies and their five core assets are copied verbatim by the vendor script |
+| Toolbox Portal, `https://git.add-ideas.de/zemion/toolbox-portal.git` | `bda9da044d61c109afd9969d357cc27f76648938` initially; `5c052bc6d1073a66600cfddc44c0e16da34bede8` for final integration | release ZIP/sidecar/lock formats, independent assembly, catalogue behavior, path security, nested deployment and production headers     | no portal application source was copied; the AV smoke harness consumes only an exact cloned Portal revision; the separate Portal worktree contains its own reviewed integration patch                            |
+| ffmpeg.wasm, `https://github.com/ffmpegwasm/ffmpeg.wasm.git`         | `f876f907c7e9b9bf51d4ed0b913a855a63ae63fc`; pinned release baseline `71aa99d37c02a7b4c435275ca9ef50e612f6efa1`         | current API, worker lifecycle, filesystem, loading, ST/MT behavior, licence documentation and build layout                              | no reference-worktree source was copied; wrapper/util remain exact npm dependencies, while the five core assets are rebuilt from the recorded source/toolchain/patch profile and verified against the build lock |

 For the **pinned** package set, the more specific upstream release tag
 `v12.15` at `71aa99d37c02a7b4c435275ca9ef50e612f6efa1` was also inspected. It
-contains `@ffmpeg/ffmpeg` 0.12.15 and core/core-mt 0.12.10. That revision's
-build selects FFmpeg n5.1.4.
+contains `@ffmpeg/ffmpeg` 0.12.15 and the source configuration for core
+0.12.10. That revision's build selects FFmpeg n5.1.4. The shipped
+`0.12.10-reviewed-stack5m.1` assets additionally apply upstream ffmpeg.wasm
+commit `b409e36475bc21f0451b5b1e1d126fa82871439a`; exact build and source
+identities are in `SOURCE.md` and `docs/FFMPEG_BUILD.md`.

-The user's active `/mnt/DATA/git/toolbox-portal` worktree still has Portal
-revision `bda9da044d61c109afd9969d357cc27f76648938` as `HEAD`, but currently
-contains a local `media-src 'self' blob:` nginx CSP patch. That mutable
-worktree state is documented for deployment testing only; it does not replace
-the immutable reference in the table.
+The active `/mnt/DATA/git/toolbox-portal` worktree has immutable revision
+`5c052bc6d1073a66600cfddc44c0e16da34bede8` as `HEAD`. Its staged cache-rule
+extension is documented separately and is not represented as a published
+revision.

 Official behavior references:

--- a/docs/RELEASE.md
+++ b/docs/RELEASE.md
@@ -11,10 +11,10 @@ The repository already declares the application licence and immutable
 third-party source identities. Before any distribution:

 1. commit the reviewed GPL-3.0-or-later source;
-2. create and verify annotated tag `v0.1.0` at that exact commit;
+2. create and verify annotated tag `v0.2.0` at that exact commit;
 3. push the commit and tag to the canonical public repository;
 4. assemble, review and publish corresponding source and exact external
-   notices for both core packages and linked libraries;
+   notices for both reviewed core profiles and linked libraries;
 5. keep the manifest/package metadata, `SOURCE.md`, ZIP and tag version aligned.

 `SOURCE.md` pins FFmpeg, ffmpeg.wasm, x264 and LAME by full commit. Do not
@@ -44,6 +44,7 @@ Normal packaging validates the root GPL version 3 text and matching
 ```sh
 npm run package:release
 npm run source:package
+npm run vendor:verify
 ```

 The legacy development-only escape hatch is retained only for checking an
@@ -56,19 +57,19 @@ npm run package:release -- --allow-unlicensed-development-smoke
 Pass `--force` only to replace the exact same-version ZIP and sidecar. Output:

 ```text
-release/av-tools-0.1.0.zip
-release/av-tools-0.1.0.zip.sha256
-release/ffmpeg-core-0.12.10-corresponding-source.tar.xz
-release/ffmpeg-core-0.12.10-corresponding-source.tar.xz.sha256
+release/av-tools-0.2.0.zip
+release/av-tools-0.2.0.zip.sha256
+release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz
+release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz.sha256
 ```

 Verify independently:

 ```sh
 node scripts/checksum-release.mjs
-(cd release && sha256sum -c ffmpeg-core-0.12.10-corresponding-source.tar.xz.sha256)
-unzip -l release/av-tools-0.1.0.zip
-tar -tJf release/ffmpeg-core-0.12.10-corresponding-source.tar.xz
+(cd release && sha256sum -c ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz.sha256)
+unzip -l release/av-tools-0.2.0.zip
+tar -tJf release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz
 ```

 The packager:
@@ -90,13 +91,13 @@ When used against a fixture without an application licence, the escape hatch add

 ## 4. Portal assembly smoke

-Use the clean reference clone beside av-tools, never the user's active Portal
-worktree:
+Use a reviewed Portal Git repository beside av-tools. The harness reads its
+exact `HEAD` and clones that revision into a temporary directory:

 ```sh
 npm run portal:smoke -- \
-  --artifact release/av-tools-0.1.0.zip \
-  --allow-known-header-gap
+  --artifact release/av-tools-0.2.0.zip \
+  --portal-root ../toolbox-portal
 ```

 The smoke harness clones the exact Portal HEAD to a temporary directory,
@@ -106,19 +107,23 @@ then verifies the generated catalogue/release records and copied FFmpeg assets.
 The temporary directory is removed unless `--keep-temp` is explicitly passed.
 No machine-specific path is committed and no Portal worktree is changed.

-Without `--allow-known-header-gap`, the clean immutable Portal reference's CSP
-omission of `media-src blob:` is a failing deployment check. The override still
-reports the gap and is only for testing archive assembly. See
-`docs/PORTAL_REQUIREMENTS.md`.
+Portal `v0.6.0`
+(`5c052bc6d1073a66600cfddc44c0e16da34bede8`) already passes the isolation,
+Blob-media CSP and explicit WASM MIME checks. Its plain-semver cache rule does
+not match the reviewed core's build-profile suffix, so the harness reports a
+cache warning. The staged Portal extension accepts only the exact reviewed
+profile in addition to plain semantic versions and rejects malformed or
+mutable-looking suffixes; a temporary clean commit containing that patch passed
+this smoke without warnings.

-The user's active `/mnt/DATA/git/toolbox-portal` worktree contains the narrow
-directive as a local patch, but the smoke intentionally does not consume that
-mutable worktree. Until the patch exists in a reviewed immutable Portal
-revision, retain the clean-reference failure/override behavior above.
+`--allow-known-header-gap` remains available only for deliberately testing an
+older Portal revision with a known required-header error. It is unnecessary
+for `v0.6.0` and must not suppress review of new gaps. See
+`docs/PORTAL_REQUIREMENTS.md`.

 ## 5. Publish only reviewed bytes

-From a clean `v0.1.0` checkout, rerun all checks, create the ZIP once, verify
+From a clean `v0.2.0` checkout, rerun all checks, create the ZIP once, verify
 the sidecar, assemble that exact ZIP through Portal, and publish the immutable
 ZIP, `.zip.sha256`, manifest, changelog, Corresponding Source and notices. Put
 its exact lowercase digest/version/id/target in a reviewed Portal lock. Never
--- a/docs/SECURITY.md
+++ b/docs/SECURITY.md
@@ -39,9 +39,10 @@ exportable diagnostics.
 Metadata is rendered as React text, never `dangerouslySetInnerHTML`. Subtitle
 text is parsed and rendered or sent through a generated local file; it is not
 inserted as HTML. Extracted URLs are inert text. The application does not open
-links from media automatically. No remote font is fetched; ASS burn-in uses
-packaged/system-generic font configuration only when the required local
-capability is available.
+links from media automatically. No remote font is fetched. Contact-sheet labels
+mount only the same-origin, size/SHA-256-verified DejaVu asset and fail closed
+without `drawtext`; ASS burn-in uses packaged/system-generic font configuration
+only when the required local capability is available.

 Preview/download URLs are `blob:` values made from local bytes. They are
 revoked on replacement, project close and unmount. Browser support for a
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -13,6 +13,7 @@ export default tseslint.config(
      'test-results',
      'playwright-report',
      'public/vendor/ffmpeg',
+      '.core-build',
    ],
  },
  {
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,18 +1,16 @@
 {
  "name": "av-tools",
-  "version": "0.1.0",
+  "version": "0.2.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "av-tools",
-      "version": "0.1.0",
+      "version": "0.2.0",
      "license": "GPL-3.0-or-later",
      "dependencies": {
        "@add-ideas/toolbox-contract": "0.2.2",
        "@add-ideas/toolbox-shell-react": "0.2.2",
-        "@ffmpeg/core": "0.12.10",
-        "@ffmpeg/core-mt": "0.12.10",
        "@ffmpeg/ffmpeg": "0.12.15",
        "@ffmpeg/util": "0.12.2",
        "fflate": "0.8.3",
@@ -718,24 +716,6 @@
        }
      }
    },
-    "node_modules/@ffmpeg/core": {
-      "version": "0.12.10",
-      "resolved": "https://registry.npmjs.org/@ffmpeg/core/-/core-0.12.10.tgz",
-      "integrity": "sha512-dzNplnn2Nxle2c2i2rrDhqcB19q9cglCkWnoMTDN9Q9l3PvdjZWd1HfSPjCNWc/p8Q3CT+Es9fWOR0UhAeYQZA==",
-      "license": "GPL-2.0-or-later",
-      "engines": {
-        "node": ">=16.x"
-      }
-    },
-    "node_modules/@ffmpeg/core-mt": {
-      "version": "0.12.10",
-      "resolved": "https://registry.npmjs.org/@ffmpeg/core-mt/-/core-mt-0.12.10.tgz",
-      "integrity": "sha512-atyRTOpa58bLCIgd6GXBZAXWyWD3AUoQyzxqjvGhp9MuSzdILtOTI62ffLswBsCnLq15lQ8IETHUpm1oe4V9FQ==",
-      "license": "GPL-2.0-or-later",
-      "engines": {
-        "node": ">=16.x"
-      }
-    },
    "node_modules/@ffmpeg/ffmpeg": {
      "version": "0.12.15",
      "resolved": "https://registry.npmjs.org/@ffmpeg/ffmpeg/-/ffmpeg-0.12.15.tgz",
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
  "name": "av-tools",
  "private": true,
-  "version": "0.1.0",
+  "version": "0.2.0",
  "description": "Local-first browser audio and video conversion and light editing with ffmpeg.wasm.",
  "license": "GPL-3.0-or-later",
  "author": "Albrecht Degering",
@@ -22,6 +22,8 @@
    "dev": "vite",
    "vendor:ffmpeg": "node scripts/copy-ffmpeg-assets.mjs",
    "vendor:verify": "node scripts/verify-ffmpeg-assets.mjs",
+    "vendor:verify-runtime": "node scripts/verify-ffmpeg-assets.mjs --runtime-only",
+    "vendor:package": "node scripts/package-reviewed-ffmpeg-core.mjs",
    "manifest:generate": "node scripts/generate-toolbox-manifest.mjs",
    "manifest:check": "node scripts/generate-toolbox-manifest.mjs --check",
    "prebuild": "npm run vendor:ffmpeg && npm run manifest:generate",
@@ -34,6 +36,9 @@
    "test": "vitest run",
    "test:watch": "vitest",
    "test:browser": "playwright test",
+    "evidence:large-preview": "playwright test tests/browser/large-media-preview.spec.ts --project=chromium --workers=1",
+    "evidence:opus": "npm run vendor:ffmpeg && npm run vendor:verify-runtime && node scripts/opus-regression.mjs",
+    "test:opus-regression": "npm run vendor:ffmpeg && npm run vendor:verify-runtime && node scripts/opus-regression.mjs --require-pass",
    "benchmark:browser": "AV_BENCHMARK=1 playwright test tests/browser/performance.spec.ts --project=chromium --workers=1",
    "fixtures:generate": "sh scripts/generate-fixtures.sh",
    "fixtures:verify": "cd tests/fixtures/generated && sha256sum -c SHA256SUMS",
@@ -42,14 +47,12 @@
    "source:package": "node scripts/package-ffmpeg-source.mjs",
    "checksum:release": "node scripts/checksum-release.mjs",
    "portal:smoke": "node scripts/portal-assembly-smoke.mjs",
-    "check": "npm run manifest:check && npm run vendor:verify && npm run typecheck && npm run lint && npm run format:check && npm run test && npm run build && npm run toolbox:check",
-    "release:artifact": "npm run check && npm run test:browser && npm run package:release"
+    "check": "npm run manifest:check && npm run vendor:verify-runtime && npm run typecheck && npm run lint && npm run format:check && npm run test && npm run build && npm run toolbox:check",
+    "release:artifact": "npm run check && npm run vendor:verify && npm run test:opus-regression && npm run test:browser && npm run package:release"
  },
  "dependencies": {
    "@add-ideas/toolbox-contract": "0.2.2",
    "@add-ideas/toolbox-shell-react": "0.2.2",
-    "@ffmpeg/core": "0.12.10",
-    "@ffmpeg/core-mt": "0.12.10",
    "@ffmpeg/ffmpeg": "0.12.15",
    "@ffmpeg/util": "0.12.2",
    "fflate": "0.8.3",
--- a/public/fonts/DejaVuSans.ttf
+++ b/public/fonts/DejaVuSans.ttf
--- a/public/toolbox-app.json
+++ b/public/toolbox-app.json
@@ -3,7 +3,7 @@
  "schemaVersion": 1,
  "id": "de.add-ideas.av-tools",
  "name": "Audio & Video Tools",
-  "version": "0.1.0",
+  "version": "0.2.0",
  "description": "Convert and lightly edit audio and video locally in the browser.",
  "entry": "./",
  "icon": "./favicon.svg",
@@ -55,10 +55,10 @@
    }
  ],
  "assets": [
-    "./vendor/ffmpeg/0.12.10/st/ffmpeg-core.js",
-    "./vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm",
-    "./vendor/ffmpeg/0.12.10/mt/ffmpeg-core.js",
-    "./vendor/ffmpeg/0.12.10/mt/ffmpeg-core.wasm",
-    "./vendor/ffmpeg/0.12.10/mt/ffmpeg-core.worker.js"
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.js",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.js",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.wasm",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.worker.js"
  ]
 }
--- a/scripts/build-reviewed-ffmpeg-core.sh
+++ b/scripts/build-reviewed-ffmpeg-core.sh
@@ -0,0 +1,420 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+set -euo pipefail
+
+usage() {
+  cat <<'EOF'
+Usage:
+  scripts/build-reviewed-ffmpeg-core.sh st|mt SOURCE_ARCHIVE EMSDK_ROOT [JOBS]
+
+Builds one private, staged FFmpeg WebAssembly core from the exact
+0.12.10 Corresponding Source archive. The only upstream source change is
+ffmpeg.wasm commit b409e36475bc21f0451b5b1e1d126fa82871439a:
+`-sSTACK_SIZE=5MB`, which fixes upstream issues #591 and #775.
+
+Output remains below .core-build/reviewed-stack5m and is never copied into the
+application automatically. Re-running resumes at verified component stamps.
+EOF
+}
+
+if [[ $# -lt 3 || $# -gt 4 ]]; then
+  usage >&2
+  exit 2
+fi
+
+MODE=$1
+SOURCE_ARCHIVE=$2
+EMSDK_ROOT=$3
+JOBS=${4:-2}
+
+if [[ "$MODE" != "st" && "$MODE" != "mt" ]]; then
+  echo "Mode must be st or mt." >&2
+  exit 2
+fi
+if [[ ! "$JOBS" =~ ^[1-8]$ ]]; then
+  echo "JOBS must be an integer from 1 to 8." >&2
+  exit 2
+fi
+
+SCRIPT_DIRECTORY=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)
+REPOSITORY_ROOT=$(cd -- "$SCRIPT_DIRECTORY/.." && pwd -P)
+SOURCE_ARCHIVE=$(realpath -- "$SOURCE_ARCHIVE")
+EMSDK_ROOT=$(realpath -- "$EMSDK_ROOT")
+
+EXPECTED_ARCHIVE_SHA256=2ab505f72be883d1257bc71cbb93880d1ade5bc029792621cb87b4ecc068399a
+EXPECTED_EMCC_SHA256=b0c9551f9155fa9c028efa24591acdfd30f02f32fb247cf9266f5f0f2ede7589
+EXPECTED_CMAKE_SHA256=ade9326f83f4996b17e2cb1bbfe4848df30a237ef5769cd3c00239b9f0d3ec58
+EXPECTED_SOURCE_ROOT=ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source
+SOURCE_DATE_EPOCH=1736208000
+
+if [[ ! -f "$SOURCE_ARCHIVE" || -L "$SOURCE_ARCHIVE" ]]; then
+  echo "SOURCE_ARCHIVE must be a regular, non-symlink file." >&2
+  exit 2
+fi
+if [[ ! -d "$EMSDK_ROOT" || -L "$EMSDK_ROOT" ]]; then
+  echo "EMSDK_ROOT must be a real directory." >&2
+  exit 2
+fi
+
+actual_archive_sha256=$(sha256sum -- "$SOURCE_ARCHIVE" | cut -d' ' -f1)
+if [[ "$actual_archive_sha256" != "$EXPECTED_ARCHIVE_SHA256" ]]; then
+  echo "Corresponding Source archive SHA-256 mismatch." >&2
+  exit 1
+fi
+
+# shellcheck disable=SC1091
+source "$EMSDK_ROOT/emsdk_env.sh" >/dev/null
+export PATH="$REPOSITORY_ROOT/scripts/build-tools:$PATH"
+if [[ -z "${AV_REVIEWED_CMAKE_BIN:-}" ]]; then
+  echo "AV_REVIEWED_CMAKE_BIN must identify the exact CMake 3.27.9 binary directory." >&2
+  exit 2
+fi
+AV_REVIEWED_CMAKE_BIN=$(realpath -- "$AV_REVIEWED_CMAKE_BIN")
+if [[ ! -d "$AV_REVIEWED_CMAKE_BIN" || -L "$AV_REVIEWED_CMAKE_BIN" ]]; then
+  echo "AV_REVIEWED_CMAKE_BIN must be a real directory." >&2
+  exit 2
+fi
+if [[ $(sha256sum -- "$AV_REVIEWED_CMAKE_BIN/cmake" | cut -d' ' -f1) != "$EXPECTED_CMAKE_SHA256" ]]; then
+  echo "CMake binary SHA-256 mismatch; exact PyPI CMake 3.27.9 is required." >&2
+  exit 1
+fi
+export PATH="$AV_REVIEWED_CMAKE_BIN:$PATH"
+EMCC=$(realpath -- "$EMSDK_ROOT/upstream/emscripten/emcc")
+actual_emcc_sha256=$(sha256sum -- "$EMCC" | cut -d' ' -f1)
+if [[ "$actual_emcc_sha256" != "$EXPECTED_EMCC_SHA256" ]]; then
+  echo "Emscripten compiler SHA-256 mismatch; activate exact version 3.1.40." >&2
+  exit 1
+fi
+if ! "$EMCC" --version | head -1 | grep -Fq \
+  "3.1.40 (5c27e79dd0a9c4e27ef2326841698cdd4f6b5784)"; then
+  echo "Emscripten identity mismatch; exact version 3.1.40 is required." >&2
+  exit 1
+fi
+if [[ $(cmake --version | head -1) != "cmake version 3.27.9" ]]; then
+  echo "CMake identity mismatch; exact version 3.27.9 is required." >&2
+  exit 1
+fi
+
+BUILD_PARENT="$REPOSITORY_ROOT/.core-build/reviewed-stack5m"
+MODE_ROOT="$BUILD_PARENT/$MODE"
+EXTRACT_ROOT="$MODE_ROOT/source"
+SOURCE_ROOT="$EXTRACT_ROOT/$EXPECTED_SOURCE_ROOT/sources"
+INSTALL_DIR="$MODE_ROOT/install"
+OUTPUT_DIR="$MODE_ROOT/output"
+STAMP_DIR="$MODE_ROOT/stamps"
+
+case "$MODE_ROOT" in
+  "$REPOSITORY_ROOT"/.core-build/reviewed-stack5m/st | \
+  "$REPOSITORY_ROOT"/.core-build/reviewed-stack5m/mt) ;;
+  *)
+    echo "Refusing an unexpected build directory: $MODE_ROOT" >&2
+    exit 1
+    ;;
+esac
+
+mkdir -p -- "$MODE_ROOT" "$STAMP_DIR"
+if [[ ! -f "$STAMP_DIR/source-prepared" ]]; then
+  if [[ -e "$EXTRACT_ROOT" ]]; then
+    echo "Incomplete source staging already exists at $EXTRACT_ROOT." >&2
+    echo "Remove only that private mode directory to restart it." >&2
+    exit 1
+  fi
+  mkdir -p -- "$EXTRACT_ROOT"
+  tar -xf "$SOURCE_ARCHIVE" -C "$EXTRACT_ROOT"
+
+  lock="$EXTRACT_ROOT/$EXPECTED_SOURCE_ROOT/SOURCE_LOCK.json"
+  node -e '
+    const fs = require("node:fs");
+    const lock = JSON.parse(fs.readFileSync(process.argv[1], "utf8"));
+    const expected = new Map([
+      ["ffmpeg.wasm", "71aa99d37c02a7b4c435275ca9ef50e612f6efa1"],
+      ["FFmpeg", "4729204c17f756e186d622060088371d10b34f7e"],
+      ["Opus", "e85ed7726db5d677c9c0677298ea0cb9c65bdd23"],
+    ]);
+    for (const [name, revision] of expected) {
+      const entry = lock.sources.find((candidate) => candidate.name === name);
+      if (!entry || entry.revision !== revision) {
+        throw new Error(`Unexpected ${name} source identity.`);
+      }
+    }
+  ' "$lock"
+
+  wasm_build_script="$SOURCE_ROOT/ffmpeg.wasm/build/ffmpeg-wasm.sh"
+  if grep -Fq -- "-sSTACK_SIZE=" "$wasm_build_script"; then
+    echo "Base archive unexpectedly already selects a stack size." >&2
+    exit 1
+  fi
+  sed -i \
+    '/-sUSE_SDL=2/a\  -sSTACK_SIZE=5MB                         # upstream b409e364: support libopus' \
+    "$wasm_build_script"
+  if [[ $(grep -Fc -- "-sSTACK_SIZE=5MB" "$wasm_build_script") -ne 1 ]]; then
+    echo "Could not apply the reviewed one-line stack patch exactly once." >&2
+    exit 1
+  fi
+
+  touch "$STAMP_DIR/source-prepared"
+fi
+
+# The upstream container uses unbounded `make -j`. Keep local builds bounded
+# without changing compiled source, and allow a resumed build to select a new
+# bounded job count.
+while IFS= read -r -d '' build_script; do
+  sed -E -i \
+    -e "s/ -j([1-8])?$/ -j$JOBS/" \
+    -e "s/ -j([1-8])? / -j$JOBS /g" \
+    "$build_script"
+done < <(find "$SOURCE_ROOT/ffmpeg.wasm/build" -type f -name '*.sh' -print0)
+
+# The upstream container does not provide native NASM. Some development hosts
+# do; allowing CMake to discover it would produce native x86 objects that
+# cannot be linked into WebAssembly. Make the container's effective choice
+# explicit and deterministic.
+X265_BUILD_SCRIPT="$SOURCE_ROOT/ffmpeg.wasm/build/x265.sh"
+if ! grep -Fq -- "-DENABLE_ASSEMBLY=OFF" "$X265_BUILD_SCRIPT"; then
+  sed -i \
+    '/-DENABLE_LIBNUMA=OFF/a\  -DENABLE_ASSEMBLY=OFF' \
+    "$X265_BUILD_SCRIPT"
+fi
+if [[ $(grep -Fc -- "-DENABLE_ASSEMBLY=OFF" "$X265_BUILD_SCRIPT") -ne 1 ]]; then
+  echo "Could not disable native x265 assembly exactly once." >&2
+  exit 1
+fi
+
+# Upstream builds each dependency in an isolated container stage. A cumulative
+# local prefix would otherwise let FreeType discover the already-built zlib and
+# let HarfBuzz discover FreeType. Their resulting private dependencies are not
+# present in FFmpeg's pkg-config probes and, on a developer workstation, optional
+# libraries such as libpng may even resolve to host-native /usr objects. Make the
+# isolated-stage dependency choices explicit.
+FREETYPE_BUILD_SCRIPT="$SOURCE_ROOT/ffmpeg.wasm/build/freetype2.sh"
+if ! grep -Fq -- "--with-zlib=no" "$FREETYPE_BUILD_SCRIPT"; then
+  sed -i \
+    '/--without-harfbuzz/a\  --with-zlib=no\n  --with-bzip2=no\n  --with-png=no\n  --with-brotli=no' \
+    "$FREETYPE_BUILD_SCRIPT"
+fi
+for freetype_flag in \
+  "--without-harfbuzz" \
+  "--with-zlib=no" \
+  "--with-bzip2=no" \
+  "--with-png=no" \
+  "--with-brotli=no"; do
+  if [[ $(grep -Fc -- "$freetype_flag" "$FREETYPE_BUILD_SCRIPT") -ne 1 ]]; then
+    echo "Could not select isolated FreeType dependency flags exactly once." >&2
+    exit 1
+  fi
+done
+
+HARFBUZZ_BUILD_SCRIPT="$SOURCE_ROOT/ffmpeg.wasm/build/harfbuzz.sh"
+for harfbuzz_flag in \
+  "--with-freetype=no" \
+  "--with-glib=no" \
+  "--with-gobject=no" \
+  "--with-cairo=no" \
+  "--with-icu=no" \
+  "--with-graphite2=no" \
+  "--with-uniscribe=no" \
+  "--with-directwrite=no" \
+  "--with-coretext=no"; do
+  if ! grep -Fq -- "$harfbuzz_flag" "$HARFBUZZ_BUILD_SCRIPT"; then
+    sed -i \
+      "/--enable-static/a\\  $harfbuzz_flag" \
+      "$HARFBUZZ_BUILD_SCRIPT"
+  fi
+  if [[ $(grep -Fc -- "$harfbuzz_flag" "$HARFBUZZ_BUILD_SCRIPT") -ne 1 ]]; then
+    echo "Could not select isolated HarfBuzz dependency flags exactly once." >&2
+    exit 1
+  fi
+done
+
+mkdir -p -- "$INSTALL_DIR" "$OUTPUT_DIR"
+
+export INSTALL_DIR
+export EM_PKG_CONFIG_PATH="$EMSDK/upstream/emscripten/system/lib/pkgconfig:$INSTALL_DIR/lib/pkgconfig"
+export EM_TOOLCHAIN_FILE="$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake"
+export PKG_CONFIG_PATH="$INSTALL_DIR/lib/pkgconfig:$EM_PKG_CONFIG_PATH"
+export LANG=C
+export LC_ALL=C
+export TZ=UTC
+export SOURCE_DATE_EPOCH
+export ZERO_AR_DATE=1
+
+MODE_FLAGS="-O3 -msimd128"
+if [[ "$MODE" == "st" ]]; then
+  export FFMPEG_ST=yes
+  unset FFMPEG_MT || true
+else
+  MODE_FLAGS="$MODE_FLAGS -sUSE_PTHREADS -pthread"
+  # HarfBuzz's pinned upstream build script reads this value directly under
+  # `set -u`, while the other scripts use its presence to disable threading.
+  # An exported empty value keeps both behaviours correct for the MT build.
+  export FFMPEG_ST=
+  export FFMPEG_MT=yes
+fi
+export CFLAGS="-I$INSTALL_DIR/include $MODE_FLAGS"
+export CXXFLAGS="$CFLAGS"
+export LDFLAGS="-L$INSTALL_DIR/lib $CFLAGS"
+
+FFMPEG_WASM="$SOURCE_ROOT/ffmpeg.wasm"
+
+build_component() {
+  local stamp=$1
+  local directory=$2
+  local script=$3
+  if [[ -f "$STAMP_DIR/$stamp" ]]; then
+    echo "[reviewed-core:$MODE] reuse $stamp"
+    return
+  fi
+  echo "[reviewed-core:$MODE] build $stamp"
+  (
+    cd -- "$SOURCE_ROOT/$directory"
+    if [[ "$stamp" == "libvpx" ]]; then
+      # libvpx embeds its configure command in the linked library. A relative
+      # prefix keeps that shipped identity independent of the checkout path
+      # while still installing into this mode's private prefix.
+      INSTALL_DIR=../../../../install \
+        CFLAGS="-I../../../../install/include $MODE_FLAGS" \
+        CXXFLAGS="-I../../../../install/include $MODE_FLAGS" \
+        LDFLAGS="-L../../../../install/lib -I../../../../install/include $MODE_FLAGS" \
+        bash "$FFMPEG_WASM/build/$script"
+    else
+      bash "$FFMPEG_WASM/build/$script"
+    fi
+  )
+  touch "$STAMP_DIR/$stamp"
+}
+
+if [[ ! -f "$STAMP_DIR/sdl2" ]]; then
+  if [[ "$MODE" == "st" ]]; then
+    embuilder build sdl2
+  else
+    embuilder build sdl2-mt
+  fi
+  touch "$STAMP_DIR/sdl2"
+fi
+
+build_component x264 x264 x264.sh
+build_component x265 x265 x265.sh
+build_component libvpx libvpx libvpx.sh
+build_component lame lame lame.sh
+build_component ogg ogg ogg.sh
+build_component theora theora theora.sh
+build_component opus opus opus.sh
+build_component vorbis vorbis vorbis.sh
+build_component zlib zlib zlib.sh
+build_component libwebp libwebp libwebp.sh
+build_component freetype2 freetype2 freetype2.sh
+build_component fribidi fribidi fribidi.sh
+build_component harfbuzz harfbuzz harfbuzz.sh
+build_component libass libass libass.sh
+build_component zimg zimg zimg.sh
+
+# Configuration probes from Autotools projects must never smuggle host-native
+# include/library paths into the reviewed WebAssembly link.
+if grep -R -E -n -- \
+  '/usr/(lib|include)|/lib/(x86_64|i[3-6]86)-linux-gnu' \
+  "$INSTALL_DIR/lib/pkgconfig" "$INSTALL_DIR/lib"/*.la; then
+  echo "A staged dependency recorded a host-native build path." >&2
+  exit 1
+fi
+if emnm "$INSTALL_DIR/lib/libfreetype.a" |
+  grep -F -- " U png_" >/dev/null; then
+  echo "FreeType unexpectedly retained an unbundled libpng dependency." >&2
+  exit 1
+fi
+if emnm "$INSTALL_DIR/lib/libfreetype.a" |
+  grep -E -- ' U (inflate|BZ2_|Brotli)' >/dev/null; then
+  echo "FreeType unexpectedly retained a cross-stage compression dependency." >&2
+  exit 1
+fi
+
+FFMPEG_SOURCE="$SOURCE_ROOT/FFmpeg"
+# FFmpeg records --extra-cflags in `ffmpeg -buildconf`. Use a path relative to
+# its source root so the shipped runtime identity is independent of the
+# maintainer's checkout location. Dependency builds above retain their
+# absolute private staging prefix; only the final FFmpeg configuration is
+# embedded in the distributed core.
+FFMPEG_INSTALL_RELATIVE=../../../../install
+export CFLAGS="-I$FFMPEG_INSTALL_RELATIVE/include $MODE_FLAGS"
+export CXXFLAGS="$CFLAGS"
+export LDFLAGS="-L$INSTALL_DIR/lib $CFLAGS"
+if [[ ! -f "$STAMP_DIR/ffmpeg" ]]; then
+  echo "[reviewed-core:$MODE] build FFmpeg"
+  (
+    cd -- "$FFMPEG_SOURCE"
+    bash "$FFMPEG_WASM/build/ffmpeg.sh" \
+      --enable-gpl \
+      --enable-libx264 \
+      --enable-libx265 \
+      --enable-libvpx \
+      --enable-libmp3lame \
+      --enable-libtheora \
+      --enable-libvorbis \
+      --enable-libopus \
+      --enable-zlib \
+      --enable-libwebp \
+      --enable-libfreetype \
+      --enable-libfribidi \
+      --enable-libass \
+      --enable-libzimg
+  )
+  touch "$STAMP_DIR/ffmpeg"
+fi
+
+if [[ ! -f "$STAMP_DIR/core" ]]; then
+  echo "[reviewed-core:$MODE] link ffmpeg-core with 5 MiB stack"
+  mkdir -p -- "$FFMPEG_SOURCE/src"
+  cp -a -- "$FFMPEG_WASM/src/bind" "$FFMPEG_SOURCE/src/"
+  cp -a -- "$FFMPEG_WASM/src/fftools" "$FFMPEG_SOURCE/src/"
+  cp -- "$FFMPEG_WASM/build/ffmpeg-wasm.sh" "$FFMPEG_SOURCE/build-reviewed-core.sh"
+  (
+    cd -- "$FFMPEG_SOURCE"
+    bash ./build-reviewed-core.sh \
+      -lx264 \
+      -lx265 \
+      -lvpx \
+      -lmp3lame \
+      -logg \
+      -ltheora \
+      -lvorbis \
+      -lvorbisenc \
+      -lvorbisfile \
+      -lopus \
+      -lz \
+      -lwebpmux \
+      -lwebp \
+      -lsharpyuv \
+      -lfreetype \
+      -lfribidi \
+      -lharfbuzz \
+      -lass \
+      -lzimg \
+      -sEXPORT_ES6 \
+      -o "$OUTPUT_DIR/ffmpeg-core.js"
+  )
+  touch "$STAMP_DIR/core"
+fi
+
+expected_files=(ffmpeg-core.js ffmpeg-core.wasm)
+if [[ "$MODE" == "mt" ]]; then
+  expected_files+=(ffmpeg-core.worker.js)
+fi
+for expected_file in "${expected_files[@]}"; do
+  if [[ ! -s "$OUTPUT_DIR/$expected_file" || -L "$OUTPUT_DIR/$expected_file" ]]; then
+    echo "Missing staged output: $OUTPUT_DIR/$expected_file" >&2
+    exit 1
+  fi
+  if grep -aFq -- "$REPOSITORY_ROOT" "$OUTPUT_DIR/$expected_file" ||
+    grep -aFq -- "$EMSDK_ROOT" "$OUTPUT_DIR/$expected_file"; then
+    echo "Staged output leaks a maintainer-local build path: $expected_file" >&2
+    exit 1
+  fi
+done
+
+(
+  cd -- "$OUTPUT_DIR"
+  sha256sum -- "${expected_files[@]}" >SHA256SUMS
+)
+
+echo "[reviewed-core:$MODE] staged outputs"
+cat "$OUTPUT_DIR/SHA256SUMS"
--- a/scripts/build-tools/install
+++ b/scripts/build-tools/install
@@ -0,0 +1,99 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# A deliberately small `install(1)` compatibility wrapper for build trees on
+# filesystems that map every created file to a shared owner and reject chmod.
+# It is used only inside the private reviewed-core build. The final asset pack
+# is hash-verified, and executable permission bits are irrelevant to browser
+# JavaScript/WebAssembly files.
+
+set -euo pipefail
+
+directory_mode=false
+create_leading=false
+target_directory=
+operands=()
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    -d)
+      directory_mode=true
+      shift
+      ;;
+    -D)
+      create_leading=true
+      shift
+      ;;
+    -c | -p | -s | -v)
+      shift
+      ;;
+    -m | -o | -g)
+      if [[ $# -lt 2 ]]; then
+        echo "install wrapper: $1 requires a value" >&2
+        exit 2
+      fi
+      shift 2
+      ;;
+    -m* | -o* | -g*)
+      shift
+      ;;
+    -t)
+      if [[ $# -lt 2 ]]; then
+        echo "install wrapper: -t requires a directory" >&2
+        exit 2
+      fi
+      target_directory=$2
+      shift 2
+      ;;
+    --)
+      shift
+      operands+=("$@")
+      break
+      ;;
+    -*)
+      echo "install wrapper: unsupported option $1" >&2
+      exit 2
+      ;;
+    *)
+      operands+=("$1")
+      shift
+      ;;
+  esac
+done
+
+if $directory_mode; then
+  if [[ ${#operands[@]} -eq 0 ]]; then
+    echo "install wrapper: -d requires at least one directory" >&2
+    exit 2
+  fi
+  mkdir -p -- "${operands[@]}"
+  exit 0
+fi
+
+if [[ -n "$target_directory" ]]; then
+  if [[ ${#operands[@]} -eq 0 ]]; then
+    echo "install wrapper: -t requires at least one source" >&2
+    exit 2
+  fi
+  mkdir -p -- "$target_directory"
+  cp -f -- "${operands[@]}" "$target_directory/"
+  exit 0
+fi
+
+if [[ ${#operands[@]} -lt 2 ]]; then
+  echo "install wrapper: expected source and destination" >&2
+  exit 2
+fi
+
+destination=${operands[-1]}
+unset 'operands[-1]'
+if $create_leading; then
+  mkdir -p -- "$(dirname -- "$destination")"
+fi
+
+if [[ ${#operands[@]} -gt 1 || -d "$destination" ]]; then
+  mkdir -p -- "$destination"
+  cp -f -- "${operands[@]}" "$destination/"
+else
+  cp -f -- "${operands[0]}" "$destination"
+fi
--- a/scripts/copy-ffmpeg-assets.mjs
+++ b/scripts/copy-ffmpeg-assets.mjs
@@ -1,138 +1,203 @@
 import { createHash } from 'node:crypto';
-import { cp, mkdir, readFile, rm, writeFile } from 'node:fs/promises';
-import { dirname, join, relative } from 'node:path';
+import { lstat, mkdir, readFile, rm, writeFile } from 'node:fs/promises';
+import path from 'node:path';
 import { fileURLToPath } from 'node:url';
+import { unzipSync } from 'fflate';

-const repositoryRoot = join(dirname(fileURLToPath(import.meta.url)), '..');
-const expectedVersion = '0.12.10';
-const outputRoot = join(
-  repositoryRoot,
-  'public',
-  'vendor',
-  'ffmpeg',
-  expectedVersion
+const repositoryRoot = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  '..'
 );
-
-const packages = [
-  {
-    packageName: '@ffmpeg/core',
-    mode: 'st',
-    files: ['ffmpeg-core.js', 'ffmpeg-core.wasm'],
-  },
-  {
-    packageName: '@ffmpeg/core-mt',
-    mode: 'mt',
-    files: ['ffmpeg-core.js', 'ffmpeg-core.wasm', 'ffmpeg-core.worker.js'],
-  },
-];
-
-const expectedHashes = new Map([
-  [
-    '@ffmpeg/core:ffmpeg-core.js',
-    '67a48f11645f85439f3fde4f2119042c16b374b910206b7a7a24f342e28dcae3',
-  ],
-  [
-    '@ffmpeg/core:ffmpeg-core.wasm',
-    '9f57947a5bd530d8f00c5b3f2cb2a3492faa7e5d823315342d6a8656d0a6b7b7',
-  ],
-  [
-    '@ffmpeg/core-mt:ffmpeg-core.js',
-    '270a2e6ff945e173238610669a3f7132df5f9c52698a9bf708cf5c2ab6bda0de',
-  ],
-  [
-    '@ffmpeg/core-mt:ffmpeg-core.wasm',
-    'be2c97605366b78f3f13e21b52e81a55a79e1f29c133b03a68ec187b1a2ec41a',
-  ],
-  [
-    '@ffmpeg/core-mt:ffmpeg-core.worker.js',
-    'f77898d631dc010b45c29c23cb4379c611a7d7b131bf591d08a656bb729a4ca3',
-  ],
+const lockPath = path.join(
+  repositoryRoot,
+  'scripts',
+  'reviewed-ffmpeg-core-lock.json'
+);
+const maximumArchiveBytes = 64 * 1024 * 1024;
+const maximumAssetBytes = 64 * 1024 * 1024;
+const requiredAssetPaths = new Set([
+  'st/ffmpeg-core.js',
+  'st/ffmpeg-core.wasm',
+  'mt/ffmpeg-core.js',
+  'mt/ffmpeg-core.wasm',
+  'mt/ffmpeg-core.worker.js',
 ]);

-async function loadPackageVersion(packageName) {
-  const packagePath = join(
-    repositoryRoot,
-    'node_modules',
-    ...packageName.split('/'),
-    'package.json'
+function sha256(bytes) {
+  return createHash('sha256').update(bytes).digest('hex');
+}
+
+function assertSafeRelativePath(value) {
+  if (
+    typeof value !== 'string' ||
+    value.length === 0 ||
+    value.includes('\\') ||
+    value.includes('\0') ||
+    value.startsWith('/') ||
+    path.posix.normalize(value) !== value ||
+    value.split('/').some((part) => !part || part === '.' || part === '..')
+  ) {
+    throw new Error(`Unsafe reviewed-core path: ${String(value)}`);
+  }
+  return value;
+}
+
+async function requireRealDirectory(directory, create = false) {
+  let details = await lstat(directory).catch((error) => {
+    if (error && typeof error === 'object' && error.code === 'ENOENT') {
+      return undefined;
+    }
+    throw error;
+  });
+  if (!details && create) {
+    await mkdir(directory);
+    details = await lstat(directory);
+  }
+  if (!details || details.isSymbolicLink() || !details.isDirectory()) {
+    throw new Error(`Required directory is unsafe: ${directory}`);
+  }
+}
+
+const lock = JSON.parse(await readFile(lockPath, 'utf8'));
+const lockedAssetPaths = new Set(
+  Array.isArray(lock.assets) ? lock.assets.map((asset) => asset.path) : []
 );
-  const parsed = JSON.parse(await readFile(packagePath, 'utf8'));
-  if (parsed.version !== expectedVersion) {
+if (
+  lock.schemaVersion !== 1 ||
+  typeof lock.buildId !== 'string' ||
+  !/^[a-zA-Z0-9._-]+$/.test(lock.buildId) ||
+  lock.coreVersion !== '0.12.10' ||
+  lock.profile !== 'reviewed-stack5m' ||
+  lock.sourceArchive?.path !==
+    'release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz' ||
+  !/^[a-f0-9]{64}$/.test(lock.sourceArchive?.sha256 ?? '') ||
+  lock.sourceLock?.path !== 'scripts/ffmpeg-source-lock.json' ||
+  !/^[a-f0-9]{64}$/.test(lock.sourceLock?.sha256 ?? '') ||
+  lock.buildDriver?.path !== 'scripts/build-reviewed-ffmpeg-core.sh' ||
+  !/^[a-f0-9]{64}$/.test(lock.buildDriver?.sha256 ?? '') ||
+  lock.patch?.upstreamCommit !== 'b409e36475bc21f0451b5b1e1d126fa82871439a' ||
+  lock.patch?.stackSizeBytes !== 5 * 1024 * 1024 ||
+  typeof lock.opusRegression?.singleThread !== 'boolean' ||
+  typeof lock.opusRegression?.multiThread !== 'boolean' ||
+  !Array.isArray(lock.assets) ||
+  lock.assets.length !== 5 ||
+  lock.assets.some(
+    (asset) =>
+      !requiredAssetPaths.has(asset.path) ||
+      !Number.isSafeInteger(asset.bytes) ||
+      asset.bytes < 1 ||
+      asset.bytes > maximumAssetBytes ||
+      !/^[a-f0-9]{64}$/.test(asset.sha256 ?? '')
+  ) ||
+  lockedAssetPaths.size !== requiredAssetPaths.size ||
+  [...requiredAssetPaths].some((assetPath) => !lockedAssetPaths.has(assetPath))
+) {
+  throw new Error(`Invalid reviewed FFmpeg core lock: ${lockPath}`);
+}
+
+const artifactRelativePath = assertSafeRelativePath(lock.artifact?.path);
+if (artifactRelativePath !== `vendor/ffmpeg-core-${lock.buildId}.zip`) {
+  throw new Error('Reviewed-core artifact path and build identity disagree.');
+}
+const artifact = await readFile(
+  path.join(repositoryRoot, ...artifactRelativePath.split('/'))
+);
+if (
+  artifact.byteLength < 1 ||
+  artifact.byteLength > maximumArchiveBytes ||
+  artifact.byteLength !== lock.artifact.bytes ||
+  sha256(artifact) !== lock.artifact.sha256
+) {
+  throw new Error('Reviewed FFmpeg core archive failed locked verification.');
+}
+
+const lockedArchiveEntries = new Map(
+  lock.assets.map((asset) => [asset.path, asset])
+);
+const archiveEntries = new Set();
+const uncompressed = unzipSync(artifact, {
+  filter: (entry) => {
+    const relative = assertSafeRelativePath(entry.name);
+    const locked = lockedArchiveEntries.get(relative);
+    if (
+      !locked ||
+      archiveEntries.has(relative) ||
+      entry.originalSize !== locked.bytes ||
+      entry.originalSize < 1 ||
+      entry.originalSize > maximumAssetBytes ||
+      entry.size < 1 ||
+      entry.size > maximumArchiveBytes
+    ) {
      throw new Error(
-      `${packageName} ${parsed.version ?? '<unknown>'} is installed; expected exactly ${expectedVersion}`
+        `Reviewed FFmpeg core archive has an unexpected entry: ${entry.name}`
      );
    }
-}
-
-async function copyAsset(packageName, mode, fileName) {
-  const source = join(
-    repositoryRoot,
-    'node_modules',
-    ...packageName.split('/'),
-    'dist',
-    'esm',
-    fileName
-  );
-  const destination = join(outputRoot, mode, fileName);
-  const sourceBytes = await readFile(source).catch((error) => {
-    throw new Error(`Required FFmpeg asset is missing: ${source}`, {
-      cause: error,
-    });
-  });
-  const sourceDigest = createHash('sha256').update(sourceBytes).digest('hex');
-  const expectedDigest = expectedHashes.get(`${packageName}:${fileName}`);
-  if (!expectedDigest || sourceDigest !== expectedDigest) {
-    throw new Error(
-      `Pinned FFmpeg asset checksum mismatch for ${packageName}/${fileName}`
-    );
-  }
-
-  await mkdir(dirname(destination), { recursive: true });
-  await cp(source, destination, {
-    dereference: true,
-    errorOnExist: false,
-    force: true,
-    preserveTimestamps: false,
-  });
-
-  const destinationBytes = await readFile(destination);
-  if (!sourceBytes.equals(destinationBytes)) {
-    throw new Error(`Copied FFmpeg asset differs from its source: ${fileName}`);
-  }
-
-  return {
-    path: relative(outputRoot, destination).replaceAll('\\', '/'),
-    bytes: destinationBytes.byteLength,
-    sha256: sourceDigest,
-  };
-}
-
-await rm(outputRoot, { force: true, recursive: true });
-
-const assets = [];
-for (const entry of packages) {
-  await loadPackageVersion(entry.packageName);
-  for (const fileName of entry.files) {
-    assets.push(await copyAsset(entry.packageName, entry.mode, fileName));
-  }
-}
-
-assets.sort((left, right) => left.path.localeCompare(right.path, 'en'));
-const versionManifest = {
-  schemaVersion: 1,
-  coreVersion: expectedVersion,
-  packages: {
-    '@ffmpeg/core': expectedVersion,
-    '@ffmpeg/core-mt': expectedVersion,
+    archiveEntries.add(relative);
+    return true;
  },
-  assets,
-};
+});
+if (archiveEntries.size !== lockedArchiveEntries.size) {
+  throw new Error('Reviewed FFmpeg core archive is missing an expected entry.');
+}

+const vendorRoot = path.join(repositoryRoot, 'public', 'vendor', 'ffmpeg');
+const outputRoot = path.join(vendorRoot, lock.buildId);
+await requireRealDirectory(repositoryRoot);
+await requireRealDirectory(path.join(repositoryRoot, 'public'));
+await requireRealDirectory(path.join(repositoryRoot, 'public', 'vendor'), true);
+const existingVendorRoot = await lstat(vendorRoot).catch((error) => {
+  if (error && typeof error === 'object' && error.code === 'ENOENT') {
+    return undefined;
+  }
+  throw error;
+});
+if (
+  existingVendorRoot &&
+  (existingVendorRoot.isSymbolicLink() || !existingVendorRoot.isDirectory())
+) {
+  throw new Error(`Generated FFmpeg vendor root is unsafe: ${vendorRoot}`);
+}
+await rm(vendorRoot, { force: true, recursive: true });
+
+for (const asset of lock.assets) {
+  const relativeAssetPath = assertSafeRelativePath(asset.path);
+  const bytes = uncompressed[relativeAssetPath];
+  if (
+    !bytes ||
+    bytes.byteLength < 1 ||
+    bytes.byteLength > maximumAssetBytes ||
+    bytes.byteLength !== asset.bytes ||
+    sha256(bytes) !== asset.sha256
+  ) {
+    throw new Error(
+      `Reviewed FFmpeg core entry failed locked verification: ${asset.path}`
+    );
+  }
+  const destination = path.join(outputRoot, ...relativeAssetPath.split('/'));
+  await mkdir(path.dirname(destination), { recursive: true });
+  await writeFile(destination, bytes, { flag: 'wx', mode: 0o644 });
+}
+
+const versionManifest = {
+  schemaVersion: 2,
+  buildId: lock.buildId,
+  profile: lock.profile,
+  coreVersion: lock.coreVersion,
+  ffmpegVersion: lock.ffmpegVersion,
+  sourceArchive: lock.sourceArchive,
+  sourceLock: lock.sourceLock,
+  buildDriver: lock.buildDriver,
+  toolchain: lock.toolchain,
+  patch: lock.patch,
+  opusRegression: lock.opusRegression,
+  assets: lock.assets,
+};
 await writeFile(
-  join(outputRoot, 'version.json'),
-  `${JSON.stringify(versionManifest, null, 2)}\n`
+  path.join(outputRoot, 'version.json'),
+  `${JSON.stringify(versionManifest, null, 2)}\n`,
+  { flag: 'wx', mode: 0o644 }
 );

 console.log(
-  `Copied ${assets.length} pinned FFmpeg assets to ${relative(repositoryRoot, outputRoot)}`
+  `Verified and unpacked ${lock.assets.length} reviewed FFmpeg assets to ${path.relative(repositoryRoot, outputRoot)}`
 );
--- a/scripts/ffmpeg-source-README.md
+++ b/scripts/ffmpeg-source-README.md
@@ -1,7 +1,9 @@
 # FFmpeg WebAssembly Corresponding Source

-This archive accompanies the exact `@ffmpeg/core` and `@ffmpeg/core-mt`
-0.12.10 object code distributed by av-tools 0.1.0.
+This archive accompanies the reviewed single-thread and multithread FFmpeg
+WebAssembly core profile distributed by av-tools. The profile retains the
+upstream core version 0.12.10 and FFmpeg n5.1.4 identities, but it is rebuilt
+from source rather than copied from the published `@ffmpeg/core` packages.

 `SOURCE_LOCK.json` records the immutable Git commit for ffmpeg.wasm, FFmpeg and
 every external library selected by the upstream v12.15 build. The source trees
@@ -18,10 +20,15 @@ The original build-control files are in `sources/ffmpeg.wasm/`, including:
 - `build/ffmpeg-wasm.sh`;
 - the other dependency scripts under `build/`.

-The upstream build selects Emscripten SDK 3.1.40 and FFmpeg n5.1.4. av-tools
-does not modify the five published JavaScript/WebAssembly core assets. Their
-exact sizes, hashes and embedded configure arguments are recorded in the
-application's `SOURCE.md` and `docs/FFMPEG_BUILD.md`.
+The build uses Emscripten SDK 3.1.40 and FFmpeg n5.1.4. Its one source patch
+applies upstream ffmpeg.wasm commit
+`b409e36475bc21f0451b5b1e1d126fa82871439a`, which raises the Emscripten stack
+to 5 MiB and fixes the libopus encode failure reported upstream. The tracked
+`scripts/build-reviewed-ffmpeg-core.sh` driver in the matching av-tools source
+release also isolates optional host dependencies and records the exact
+toolchain identities. The generated assets' exact sizes, hashes and embedded
+configure arguments are recorded in the application's `SOURCE.md`,
+`scripts/reviewed-ffmpeg-core-lock.json` and `docs/FFMPEG_BUILD.md`.

 The source archive preserves each component's own licence and copyright
 notices. av-tools itself is distributed separately under
@@ -37,14 +44,11 @@ test "$(git -C source-check rev-parse FETCH_HEAD)" = "<revision>"
 ```

 The included ffmpeg.wasm Dockerfile documents the historical upstream build,
-but still names remote tags and branches. It is not a turnkey offline or
-byte-for-byte reproducible build recipe. To reconstruct a pinned build,
-adapt each remote `ADD` to use the corresponding bundled source tree. Replace
-the zimg `git clone -b ... --recursive` step with the bundled `sources/zimg/`
-tree, which already contains its pinned GoogleTest submodule at
-`test/extra/googletest/`. Keep the included build scripts and Emscripten
-version unchanged. The upstream targets are `make prd` for single-thread and
-`make prd-mt` for multithread.
+but still names remote tags and branches. For the distributed reviewed
+profile, use this archive together with the matching av-tools source release
+and invoke its `scripts/build-reviewed-ffmpeg-core.sh` driver. The bundled
+`sources/zimg/` tree already contains its pinned GoogleTest submodule at
+`test/extra/googletest/`.

 General-purpose build tooling such as Git, Docker/BuildKit and the Emscripten
 3.1.40 container image is not copied into this archive.
--- a/scripts/opus-regression.mjs
+++ b/scripts/opus-regression.mjs
@@ -0,0 +1,522 @@
+import { spawn } from 'node:child_process';
+import { createHash } from 'node:crypto';
+import { readFile, stat } from 'node:fs/promises';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const SCRIPT_PATH = fileURLToPath(import.meta.url);
+const REPOSITORY_ROOT = path.resolve(path.dirname(SCRIPT_PATH), '..');
+const FIXTURE_RELATIVE_PATH = 'tests/fixtures/generated/tone.wav';
+const FIXTURE_PATH = path.join(REPOSITORY_ROOT, FIXTURE_RELATIVE_PATH);
+const EXPECTED_FIXTURE_BYTES = 32_102;
+const EXPECTED_FIXTURE_SHA256 =
+  '0fd1f54d6be2f1cc7fd778775dd29cf184770d3716cf3394bf03ed54ac264c3c';
+const DEFAULT_MODE_TIMEOUT_MILLISECONDS = 60_000;
+const RESULT_PREFIX = 'OPUS_RESULT ';
+const EVENT_PREFIX = 'OPUS_EVENT ';
+const MODES = Object.freeze(['single-thread', 'multithread']);
+
+const argumentsSet = new Set(process.argv.slice(2));
+const option = (name) =>
+  process.argv
+    .slice(2)
+    .find((argument) => argument.startsWith(`--${name}=`))
+    ?.slice(name.length + 3);
+
+function boundedInteger(value, fallback, minimum, maximum) {
+  const parsed = Number(value);
+  return Number.isSafeInteger(parsed) && parsed >= minimum && parsed <= maximum
+    ? parsed
+    : fallback;
+}
+
+function serializeError(error) {
+  if (error instanceof Error) {
+    return {
+      name: error.name,
+      message: error.message,
+      ...(error.stack ? { stack: error.stack.split('\n').slice(0, 8) } : {}),
+    };
+  }
+  return { name: 'Error', message: String(error) };
+}
+
+function emit(prefix, value) {
+  process.stdout.write(`${prefix}${JSON.stringify(value)}\n`);
+}
+
+function parsePrefixedJsonLines(text, prefix) {
+  return text
+    .split(/\r?\n/u)
+    .filter((line) => line.startsWith(prefix))
+    .flatMap((line) => {
+      try {
+        return [JSON.parse(line.slice(prefix.length))];
+      } catch {
+        return [];
+      }
+    });
+}
+
+function appendBounded(current, chunk, maximumLength = 32_768) {
+  return `${current}${chunk}`.slice(-maximumLength);
+}
+
+function terminateProcessGroup(child) {
+  if (!child.pid) return;
+  try {
+    if (process.platform === 'win32') {
+      child.kill('SIGKILL');
+    } else {
+      process.kill(-child.pid, 'SIGKILL');
+    }
+  } catch {
+    child.kill('SIGKILL');
+  }
+}
+
+async function runIsolatedMode(mode, origin, timeoutMilliseconds) {
+  const startedAt = performance.now();
+  const child = spawn(
+    process.execPath,
+    [SCRIPT_PATH, '--child', `--mode=${mode}`, `--origin=${origin}`],
+    {
+      cwd: REPOSITORY_ROOT,
+      detached: process.platform !== 'win32',
+      stdio: ['ignore', 'pipe', 'pipe'],
+    }
+  );
+  let stdout = '';
+  let stderr = '';
+  let timedOut = false;
+
+  child.stdout.setEncoding('utf8');
+  child.stderr.setEncoding('utf8');
+  child.stdout.on('data', (chunk) => {
+    stdout = appendBounded(stdout, chunk);
+    for (const event of parsePrefixedJsonLines(chunk, EVENT_PREFIX)) {
+      if (event.stage && event.stage !== 'core-log') {
+        process.stdout.write(`[opus:${mode}] ${event.stage}\n`);
+      }
+    }
+  });
+  child.stderr.on('data', (chunk) => {
+    stderr = appendBounded(stderr, chunk);
+  });
+
+  const timeout = setTimeout(() => {
+    timedOut = true;
+    terminateProcessGroup(child);
+  }, timeoutMilliseconds);
+
+  const { code, signal } = await new Promise((resolve) => {
+    child.once('close', (exitCode, exitSignal) => {
+      resolve({ code: exitCode, signal: exitSignal });
+    });
+  });
+  clearTimeout(timeout);
+
+  const elapsedMilliseconds = Math.round(performance.now() - startedAt);
+  const events = parsePrefixedJsonLines(stdout, EVENT_PREFIX);
+  const reported = parsePrefixedJsonLines(stdout, RESULT_PREFIX).at(-1);
+  if (reported) {
+    return {
+      ...reported,
+      elapsedMilliseconds,
+      process: { exitCode: code, signal },
+    };
+  }
+
+  const coreReady = events.find((event) => event.stage === 'core-ready');
+  const lastStage = [...events]
+    .reverse()
+    .find((event) => event.stage && event.stage !== 'core-log');
+  const relevantLogs = events
+    .filter((event) => event.stage === 'core-log')
+    .slice(-16)
+    .map((event) => event.message);
+  return {
+    requestedMode: mode,
+    status: 'fail',
+    failure: timedOut ? 'timeout' : 'child-exited-without-result',
+    message: timedOut
+      ? `The isolated browser did not finish within ${String(timeoutMilliseconds)} ms.`
+      : 'The isolated browser exited without a structured result.',
+    ...(coreReady?.actualMode ? { actualMode: coreReady.actualMode } : {}),
+    ...(coreReady?.ffmpegVersion
+      ? { ffmpegVersion: coreReady.ffmpegVersion }
+      : {}),
+    ...(coreReady?.capabilities
+      ? { capabilities: coreReady.capabilities }
+      : {}),
+    ...(lastStage?.stage ? { lastStage: lastStage.stage } : {}),
+    ...(relevantLogs.length > 0 ? { relevantLogs } : {}),
+    ...(stderr.trim() ? { stderr: stderr.trim().split('\n').slice(-12) } : {}),
+    elapsedMilliseconds,
+    process: { exitCode: code, signal },
+  };
+}
+
+async function fixtureIdentity() {
+  const [bytes, fixtureStat] = await Promise.all([
+    readFile(FIXTURE_PATH),
+    stat(FIXTURE_PATH),
+  ]);
+  const sha256 = createHash('sha256').update(bytes).digest('hex');
+  if (
+    fixtureStat.size !== EXPECTED_FIXTURE_BYTES ||
+    sha256 !== EXPECTED_FIXTURE_SHA256
+  ) {
+    throw new Error(
+      `Opus fixture identity mismatch: expected ${String(EXPECTED_FIXTURE_BYTES)} bytes/${EXPECTED_FIXTURE_SHA256}, received ${String(fixtureStat.size)} bytes/${sha256}.`
+    );
+  }
+  return {
+    path: FIXTURE_RELATIVE_PATH,
+    bytes: fixtureStat.size,
+    sha256,
+  };
+}
+
+async function runMain() {
+  const timeoutMilliseconds = boundedInteger(
+    option('timeout-ms') ?? process.env.AV_OPUS_REGRESSION_TIMEOUT_MS,
+    DEFAULT_MODE_TIMEOUT_MILLISECONDS,
+    10_000,
+    10 * 60_000
+  );
+  const [fixture, packageText, coreLockText] = await Promise.all([
+    fixtureIdentity(),
+    readFile(path.join(REPOSITORY_ROOT, 'package.json'), 'utf8'),
+    readFile(
+      path.join(REPOSITORY_ROOT, 'scripts', 'reviewed-ffmpeg-core-lock.json'),
+      'utf8'
+    ),
+  ]);
+  const packageManifest = JSON.parse(packageText);
+  const coreLock = JSON.parse(coreLockText);
+  const { createServer } = await import('vite');
+  const server = await createServer({
+    configFile: path.join(REPOSITORY_ROOT, 'vite.config.ts'),
+    logLevel: 'warn',
+    server: {
+      host: '127.0.0.1',
+      port: 0,
+      strictPort: false,
+    },
+  });
+
+  try {
+    await server.listen();
+    const address = server.httpServer?.address();
+    if (!address || typeof address === 'string') {
+      throw new Error('Vite did not expose a local TCP address.');
+    }
+    const origin = `http://127.0.0.1:${String(address.port)}`;
+    const modes = [];
+    for (const mode of MODES) {
+      modes.push(await runIsolatedMode(mode, origin, timeoutMilliseconds));
+    }
+    const report = {
+      schemaVersion: 2,
+      recordedAt: new Date().toISOString(),
+      browser: 'chromium',
+      wrapperVersion: packageManifest.dependencies['@ffmpeg/ffmpeg'],
+      coreVersion: coreLock.coreVersion,
+      coreBuildId: coreLock.buildId,
+      coreProfile: coreLock.profile,
+      fixture,
+      perModeTimeoutMilliseconds: timeoutMilliseconds,
+      modes,
+      safe: modes.every((result) => result.status === 'pass'),
+    };
+    process.stdout.write(`${JSON.stringify(report, null, 2)}\n`);
+    if (argumentsSet.has('--require-pass') && !report.safe) {
+      process.exitCode = 1;
+    }
+  } finally {
+    await server.close();
+  }
+}
+
+async function runBrowserMode(mode, origin) {
+  const { chromium } = await import('@playwright/test');
+  const browser = await chromium.launch({ headless: true });
+  try {
+    const page = await browser.newPage();
+    await page.exposeFunction('__reportOpusEvent', (event) => {
+      emit(EVENT_PREFIX, event);
+    });
+    await page.goto(origin, {
+      waitUntil: 'domcontentloaded',
+      timeout: 30_000,
+    });
+    return await page.evaluate(
+      async ({ fixtureUrl, requestedMode }) => {
+        const report = async (event) => {
+          await globalThis.__reportOpusEvent(event);
+        };
+        const replacePaths = (plan, context) => {
+          const replacements = new Map();
+          plan.inputs.forEach((input, index) => {
+            const actual = context.inputPaths[index];
+            if (actual) replacements.set(input.path, actual);
+          });
+          plan.outputs.forEach((output, index) => {
+            const actual = context.outputPaths[index];
+            if (actual) replacements.set(output.path, actual);
+          });
+          plan.temporaryFiles.forEach((temporary, index) => {
+            const actual = context.temporaryPaths[index];
+            if (actual) replacements.set(temporary.path, actual);
+          });
+          return plan.args.map((argument) =>
+            [...replacements].reduce(
+              (resolved, [virtualPath, actualPath]) =>
+                resolved.replaceAll(virtualPath, actualPath),
+              argument
+            )
+          );
+        };
+        const errorShape = (error) =>
+          error instanceof Error
+            ? {
+                name: error.name,
+                message: error.message,
+                ...(error.stack
+                  ? { stack: error.stack.split('\n').slice(0, 8) }
+                  : {}),
+              }
+            : { name: 'Error', message: String(error) };
+        let manager;
+        const relevantLogs = [];
+        try {
+          await report({ stage: 'module-import' });
+          const [{ EngineManager }, { buildConvertPlan }, { AUDIO_PRESETS }] =
+            await Promise.all([
+              import('/src/ffmpeg/EngineManager.ts'),
+              import('/src/commands/convert.ts'),
+              import('/src/presets/audio-presets.ts'),
+            ]);
+          manager = new EngineManager();
+          manager.setPreference(
+            requestedMode === 'single-thread'
+              ? 'force-single-thread'
+              : 'prefer-multithread'
+          );
+          manager.onLog((event) => {
+            for (const line of event.message.split(/\r?\n/u)) {
+              if (
+                relevantLogs.length < 32 &&
+                /libopus|Output #|Stream mapping|Aborted\(\)|(?:^|\s)(?:size|progress)=|error|failed/iu.test(
+                  line
+                )
+              ) {
+                const message = line.slice(0, 600);
+                relevantLogs.push(message);
+                void report({ stage: 'core-log', message });
+              }
+            }
+          });
+
+          await report({ stage: 'fixture-fetch' });
+          const fixtureResponse = await fetch(fixtureUrl);
+          if (!fixtureResponse.ok) {
+            throw new Error(
+              `Fixture request failed with HTTP ${String(fixtureResponse.status)}.`
+            );
+          }
+          const fixtureBytes = new Uint8Array(
+            await fixtureResponse.arrayBuffer()
+          );
+          const sourceFile = new File([fixtureBytes], 'tone.wav', {
+            type: 'audio/wav',
+          });
+
+          await report({ stage: 'core-initializing' });
+          await manager.initialize();
+          const ready = manager.state;
+          if (ready.status !== 'ready') {
+            throw new Error('The FFmpeg engine did not reach ready state.');
+          }
+          const capabilities = {
+            opusMuxer: ready.capabilities.muxers.has('opus'),
+            libopusEncoder: ready.capabilities.encoders.has('libopus'),
+          };
+          await report({
+            stage: 'core-ready',
+            requestedMode,
+            actualMode: ready.mode,
+            ffmpegVersion: ready.capabilities.versionText,
+            capabilities,
+          });
+          if (ready.mode !== requestedMode) {
+            throw new Error(
+              `Requested ${requestedMode}, but the engine selected ${ready.mode}.`
+            );
+          }
+          if (!capabilities.opusMuxer || !capabilities.libopusEncoder) {
+            throw new Error(
+              'The pinned core does not advertise the Opus muxer and libopus encoder.'
+            );
+          }
+
+          const preset = AUDIO_PRESETS.find(
+            (candidate) => candidate.id === 'audio-opus'
+          );
+          if (!preset) {
+            throw new Error('The built-in audio-opus preset is missing.');
+          }
+          const plan = buildConvertPlan({
+            jobId: `opus-regression-${requestedMode}`,
+            source: {
+              id: 'tone',
+              sourceIndex: 0,
+              fileName: 'tone.wav',
+              extension: 'wav',
+            },
+            preset,
+            streamSelection: { audio: [0] },
+            expectedDurationSeconds: 1,
+            timeoutMs: 30_000,
+          });
+          await report({
+            stage: 'encode-started',
+            presetId: preset.id,
+            requirements: plan.requiredCapabilities,
+          });
+          let commandArguments = [];
+          const completed = await manager.runJob({
+            id: `opus-regression-${requestedMode}`,
+            operation: 'Opus regression',
+            coreWorkload: plan.operation,
+            inputs: [sourceFile],
+            outputs: plan.outputs.map((output) => ({
+              name: output.fileName,
+              mimeType: output.mediaType,
+            })),
+            expectedDurationSeconds: plan.expectedDurationSeconds,
+            timeoutMilliseconds: plan.timeoutMs,
+            buildArguments: (context) => {
+              commandArguments = replacePaths(plan, context);
+              void report({
+                stage: 'encode-command',
+                arguments: commandArguments,
+              });
+              return commandArguments;
+            },
+          });
+          const output = completed.outputs[0];
+          if (!output || output.bytes.byteLength === 0) {
+            throw new Error(
+              'The Opus encode did not produce non-empty output.'
+            );
+          }
+          await report({
+            stage: 'encode-finished',
+            outputBytes: output.bytes.byteLength,
+          });
+
+          const outputFile = new File([output.bytes], output.name, {
+            type: output.mimeType,
+          });
+          await report({ stage: 'reprobe-started' });
+          const probe = await manager.probe(outputFile, 15_000);
+          const probeJson = probe.json;
+          const streams = Array.isArray(probeJson?.streams)
+            ? probeJson.streams
+            : [];
+          const opusStream = streams.find(
+            (stream) =>
+              stream?.codec_type === 'audio' && stream?.codec_name === 'opus'
+          );
+          const durationSeconds = Number(
+            probeJson?.format?.duration ?? opusStream?.duration
+          );
+          if (!opusStream || !(durationSeconds > 0)) {
+            throw new Error(
+              'The generated file did not re-probe as positive-duration Opus audio.'
+            );
+          }
+          const digest = new Uint8Array(
+            await crypto.subtle.digest('SHA-256', output.bytes)
+          );
+          const outputSha256 = [...digest]
+            .map((value) => value.toString(16).padStart(2, '0'))
+            .join('');
+          await report({ stage: 'reprobe-finished', durationSeconds });
+          return {
+            requestedMode,
+            actualMode: ready.mode,
+            status: 'pass',
+            ffmpegVersion: ready.capabilities.versionText,
+            capabilities,
+            presetId: preset.id,
+            commandArguments,
+            output: {
+              name: output.name,
+              mimeType: output.mimeType,
+              bytes: output.bytes.byteLength,
+              sha256: outputSha256,
+              codecName: opusStream.codec_name,
+              codecType: opusStream.codec_type,
+              durationSeconds,
+            },
+            relevantLogs,
+          };
+        } catch (error) {
+          const state = manager?.state;
+          return {
+            requestedMode,
+            ...(state?.mode ? { actualMode: state.mode } : {}),
+            status: 'fail',
+            failure: 'browser-operation-failed',
+            error: errorShape(error),
+            relevantLogs,
+          };
+        } finally {
+          manager?.dispose();
+        }
+      },
+      {
+        fixtureUrl: `${origin}/${FIXTURE_RELATIVE_PATH}`,
+        requestedMode: mode,
+      }
+    );
+  } finally {
+    await browser.close();
+  }
+}
+
+async function runChild() {
+  const mode = option('mode');
+  const origin = option('origin');
+  if (!MODES.includes(mode) || !origin) {
+    throw new Error('Child mode requires valid --mode and --origin options.');
+  }
+  emit(EVENT_PREFIX, { stage: 'browser-launching', requestedMode: mode });
+  try {
+    const result = await runBrowserMode(mode, origin);
+    emit(RESULT_PREFIX, result);
+  } catch (error) {
+    emit(RESULT_PREFIX, {
+      requestedMode: mode,
+      status: 'fail',
+      failure: 'browser-process-failed',
+      error: serializeError(error),
+    });
+  }
+}
+
+try {
+  if (argumentsSet.has('--child')) {
+    await runChild();
+  } else {
+    await runMain();
+  }
+} catch (error) {
+  process.stderr.write(
+    `Opus regression harness failed: ${JSON.stringify(serializeError(error))}\n`
+  );
+  process.exitCode = 2;
+}
--- a/scripts/package-ffmpeg-source.mjs
+++ b/scripts/package-ffmpeg-source.mjs
@@ -18,6 +18,11 @@ import { createReadStream } from 'node:fs';

 const repositoryRoot = resolve(dirname(fileURLToPath(import.meta.url)), '..');
 const lockPath = join(repositoryRoot, 'scripts', 'ffmpeg-source-lock.json');
+const reviewedLockPath = join(
+  repositoryRoot,
+  'scripts',
+  'reviewed-ffmpeg-core-lock.json'
+);
 const readmePath = join(repositoryRoot, 'scripts', 'ffmpeg-source-README.md');
 const releaseDirectory = join(repositoryRoot, 'release');
 const force = process.argv.includes('--force');
@@ -204,7 +209,19 @@ async function publishSourcePair({

 const lock = JSON.parse(await readFile(lockPath, 'utf8'));
 assertLock(lock);
-const archiveName = `ffmpeg-core-${lock.coreVersion}-corresponding-source.tar.xz`;
+const reviewedLock = JSON.parse(await readFile(reviewedLockPath, 'utf8'));
+if (
+  reviewedLock?.schemaVersion !== 1 ||
+  reviewedLock.coreVersion !== lock.coreVersion ||
+  typeof reviewedLock.buildId !== 'string' ||
+  !/^[a-zA-Z0-9._-]+$/u.test(reviewedLock.buildId) ||
+  !reviewedLock.buildId.startsWith(`${lock.coreVersion}-`)
+) {
+  throw new Error(
+    'The reviewed-core lock does not identify a build-qualified source bundle.'
+  );
+}
+const archiveName = `ffmpeg-core-${reviewedLock.buildId}-corresponding-source.tar.xz`;
 const archivePath = join(releaseDirectory, archiveName);
 const checksumPath = `${archivePath}.sha256`;
 await ensureReleaseDirectory();
--- a/scripts/package-release.mjs
+++ b/scripts/package-release.mjs
@@ -52,8 +52,6 @@ const ffmpegLicenseCoverage = new Map([
  ['@ffmpeg/ffmpeg', 'LICENSES/ffmpeg.wasm-MIT.txt'],
  ['@ffmpeg/util', 'LICENSES/ffmpeg.wasm-MIT.txt'],
  ['@ffmpeg/types', 'LICENSES/ffmpeg.wasm-MIT.txt'],
-  ['@ffmpeg/core', 'LICENSES/GPL-2.0-or-later.txt'],
-  ['@ffmpeg/core-mt', 'LICENSES/GPL-2.0-or-later.txt'],
 ]);

 function compareText(left, right) {
@@ -479,7 +477,8 @@ function validateReleaseLayout(entries, packageJson, applicationLicense) {
    }
  }

-  const vendorManifestPath = 'vendor/ffmpeg/0.12.10/version.json';
+  const vendorBuildId = '0.12.10-reviewed-stack5m.1';
+  const vendorManifestPath = `vendor/ffmpeg/${vendorBuildId}/version.json`;
  const vendorManifestEntry = entriesByName.get(vendorManifestPath);
  if (!vendorManifestEntry) {
    throw new Error(
@@ -488,10 +487,12 @@ function validateReleaseLayout(entries, packageJson, applicationLicense) {
  }
  const vendorManifest = JSON.parse(vendorManifestEntry.data.toString('utf8'));
  if (
-    vendorManifest.schemaVersion !== 1 ||
+    vendorManifest.schemaVersion !== 2 ||
+    vendorManifest.buildId !== vendorBuildId ||
+    vendorManifest.profile !== 'reviewed-stack5m' ||
    vendorManifest.coreVersion !== '0.12.10' ||
-    vendorManifest.packages?.['@ffmpeg/core'] !== '0.12.10' ||
-    vendorManifest.packages?.['@ffmpeg/core-mt'] !== '0.12.10' ||
+    vendorManifest.opusRegression?.singleThread !== true ||
+    vendorManifest.opusRegression?.multiThread !== true ||
    !Array.isArray(vendorManifest.assets) ||
    vendorManifest.assets.length !== 5
  ) {
@@ -511,7 +512,7 @@ function validateReleaseLayout(entries, packageJson, applicationLicense) {
      );
    }
    const assetPath = safeArchivePath(
-      path.posix.join('vendor/ffmpeg/0.12.10', asset.path)
+      path.posix.join(`vendor/ffmpeg/${vendorBuildId}`, asset.path)
    );
    if (verifiedVendorPaths.has(assetPath)) {
      throw new Error(`Duplicate FFmpeg verification path: ${assetPath}`);
--- a/scripts/package-reviewed-ffmpeg-core.mjs
+++ b/scripts/package-reviewed-ffmpeg-core.mjs
@@ -0,0 +1,279 @@
+import { createHash } from 'node:crypto';
+import {
+  lstat,
+  mkdir,
+  mkdtemp,
+  readFile,
+  realpath,
+  rename,
+  rm,
+  writeFile,
+} from 'node:fs/promises';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { unzipSync, zipSync } from 'fflate';
+
+const repositoryRoot = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  '..'
+);
+const lockPath = path.join(
+  repositoryRoot,
+  'scripts',
+  'reviewed-ffmpeg-core-lock.json'
+);
+const maximumAssetBytes = 64 * 1024 * 1024;
+const fixedTimestamp = new Date(1980, 0, 1, 0, 0, 0, 0);
+const requiredAssetPaths = new Set([
+  'st/ffmpeg-core.js',
+  'st/ffmpeg-core.wasm',
+  'mt/ffmpeg-core.js',
+  'mt/ffmpeg-core.wasm',
+  'mt/ffmpeg-core.worker.js',
+]);
+
+function sha256(bytes) {
+  return createHash('sha256').update(bytes).digest('hex');
+}
+
+function assertSafeRelativePath(value) {
+  if (
+    typeof value !== 'string' ||
+    value.length === 0 ||
+    value.includes('\\') ||
+    value.includes('\0') ||
+    value.startsWith('/') ||
+    path.posix.normalize(value) !== value ||
+    value.split('/').some((part) => !part || part === '.' || part === '..')
+  ) {
+    throw new Error(`Unsafe reviewed-core path: ${String(value)}`);
+  }
+  return value;
+}
+
+async function requireRealDirectory(directory, create = false) {
+  let details = await lstat(directory).catch((error) => {
+    if (error && typeof error === 'object' && error.code === 'ENOENT') {
+      return undefined;
+    }
+    throw error;
+  });
+  if (!details && create) {
+    await mkdir(directory);
+    details = await lstat(directory);
+  }
+  if (!details || details.isSymbolicLink() || !details.isDirectory()) {
+    throw new Error(`Required directory is unsafe: ${directory}`);
+  }
+}
+
+async function readLock() {
+  const lock = JSON.parse(await readFile(lockPath, 'utf8'));
+  const lockedAssetPaths = new Set(
+    Array.isArray(lock.assets) ? lock.assets.map((asset) => asset.path) : []
+  );
+  if (
+    lock.schemaVersion !== 1 ||
+    typeof lock.buildId !== 'string' ||
+    !/^[a-zA-Z0-9._-]+$/.test(lock.buildId) ||
+    lock.coreVersion !== '0.12.10' ||
+    lock.profile !== 'reviewed-stack5m' ||
+    lock.sourceArchive?.path !==
+      'release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz' ||
+    !Number.isSafeInteger(lock.sourceArchive?.bytes) ||
+    !/^[a-f0-9]{64}$/.test(lock.sourceArchive?.sha256 ?? '') ||
+    lock.sourceLock?.path !== 'scripts/ffmpeg-source-lock.json' ||
+    !/^[a-f0-9]{64}$/.test(lock.sourceLock?.sha256 ?? '') ||
+    lock.buildDriver?.path !== 'scripts/build-reviewed-ffmpeg-core.sh' ||
+    !/^[a-f0-9]{64}$/.test(lock.buildDriver?.sha256 ?? '') ||
+    !Array.isArray(lock.assets) ||
+    lock.assets.length !== 5 ||
+    lock.assets.some(
+      (asset) =>
+        !requiredAssetPaths.has(asset.path) ||
+        !Number.isSafeInteger(asset.bytes) ||
+        asset.bytes < 1 ||
+        asset.bytes > maximumAssetBytes ||
+        !/^[a-f0-9]{64}$/.test(asset.sha256 ?? '')
+    ) ||
+    lockedAssetPaths.size !== requiredAssetPaths.size ||
+    [...requiredAssetPaths].some(
+      (assetPath) => !lockedAssetPaths.has(assetPath)
+    ) ||
+    typeof lock.artifact?.path !== 'string' ||
+    !Number.isSafeInteger(lock.artifact?.bytes) ||
+    lock.artifact.bytes < 1 ||
+    lock.artifact.bytes > 64 * 1024 * 1024 ||
+    !/^[a-f0-9]{64}$/.test(lock.artifact?.sha256 ?? '')
+  ) {
+    throw new Error(`Invalid reviewed FFmpeg core lock: ${lockPath}`);
+  }
+  return lock;
+}
+
+async function readBuildAsset(asset) {
+  const relativeAssetPath = assertSafeRelativePath(asset.path);
+  const [mode, fileName, ...extra] = relativeAssetPath.split('/');
+  if (
+    extra.length > 0 ||
+    !['st', 'mt'].includes(mode) ||
+    !['ffmpeg-core.js', 'ffmpeg-core.wasm', 'ffmpeg-core.worker.js'].includes(
+      fileName
+    )
+  ) {
+    throw new Error(`Unexpected reviewed-core asset: ${relativeAssetPath}`);
+  }
+  const outputDirectory = path.join(
+    repositoryRoot,
+    '.core-build',
+    'reviewed-stack5m',
+    mode,
+    'output'
+  );
+  const source = path.join(outputDirectory, fileName);
+  const details = await lstat(source);
+  if (details.isSymbolicLink() || !details.isFile()) {
+    throw new Error(`Reviewed-core input must be a regular file: ${source}`);
+  }
+  const canonicalOutput = await realpath(outputDirectory);
+  const canonicalSource = await realpath(source);
+  if (!canonicalSource.startsWith(`${canonicalOutput}${path.sep}`)) {
+    throw new Error(`Reviewed-core input resolves outside output: ${source}`);
+  }
+  const bytes = await readFile(canonicalSource);
+  if (
+    bytes.byteLength < 1 ||
+    bytes.byteLength > maximumAssetBytes ||
+    bytes.byteLength !== asset.bytes ||
+    sha256(bytes) !== asset.sha256
+  ) {
+    throw new Error(`Reviewed-core build does not match lock: ${asset.path}`);
+  }
+  return bytes;
+}
+
+function verifyArchiveEntries(archive, lock) {
+  const lockedEntries = new Map(
+    lock.assets.map((asset) => [asset.path, asset])
+  );
+  const seen = new Set();
+  const uncompressed = unzipSync(archive, {
+    filter: (entry) => {
+      const relative = assertSafeRelativePath(entry.name);
+      const locked = lockedEntries.get(relative);
+      if (
+        !locked ||
+        seen.has(relative) ||
+        entry.originalSize !== locked.bytes ||
+        entry.originalSize < 1 ||
+        entry.originalSize > maximumAssetBytes ||
+        entry.size < 1 ||
+        entry.size > 64 * 1024 * 1024
+      ) {
+        throw new Error(
+          `Reviewed-core archive contains an unexpected entry: ${entry.name}`
+        );
+      }
+      seen.add(relative);
+      return true;
+    },
+  });
+  if (seen.size !== lockedEntries.size) {
+    throw new Error('Reviewed-core archive is missing an expected entry.');
+  }
+  for (const asset of lock.assets) {
+    const bytes = uncompressed[asset.path];
+    if (
+      !bytes ||
+      bytes.byteLength !== asset.bytes ||
+      sha256(bytes) !== asset.sha256
+    ) {
+      throw new Error(
+        `Reviewed-core archive entry does not match lock: ${asset.path}`
+      );
+    }
+  }
+}
+
+const lock = await readLock();
+const buildDriver = await readFile(
+  path.join(repositoryRoot, ...lock.buildDriver.path.split('/'))
+);
+if (sha256(buildDriver) !== lock.buildDriver.sha256) {
+  throw new Error(
+    'Reviewed-core build driver does not match its locked identity.'
+  );
+}
+const sourceLock = await readFile(
+  path.join(repositoryRoot, ...lock.sourceLock.path.split('/'))
+);
+if (sha256(sourceLock) !== lock.sourceLock.sha256) {
+  throw new Error('FFmpeg source lock does not match its locked identity.');
+}
+const sourceArchive = await readFile(
+  path.join(repositoryRoot, ...lock.sourceArchive.path.split('/'))
+);
+if (
+  sourceArchive.byteLength !== lock.sourceArchive.bytes ||
+  sha256(sourceArchive) !== lock.sourceArchive.sha256
+) {
+  throw new Error(
+    'Reviewed-core Corresponding Source archive does not match its locked identity.'
+  );
+}
+const artifactRelativePath = assertSafeRelativePath(lock.artifact.path);
+const expectedArtifactRelativePath = `vendor/ffmpeg-core-${lock.buildId}.zip`;
+if (artifactRelativePath !== expectedArtifactRelativePath) {
+  throw new Error(
+    `Reviewed-core artifact path must be ${expectedArtifactRelativePath}.`
+  );
+}
+const artifactPath = path.join(
+  repositoryRoot,
+  ...artifactRelativePath.split('/')
+);
+const entries = {};
+for (const asset of [...lock.assets].sort((left, right) =>
+  left.path.localeCompare(right.path, 'en')
+)) {
+  entries[asset.path] = [
+    await readBuildAsset(asset),
+    { level: 9, mtime: fixedTimestamp },
+  ];
+}
+const archive = Buffer.from(zipSync(entries, { level: 9 }));
+verifyArchiveEntries(archive, lock);
+const archiveDigest = sha256(archive);
+if (
+  archive.byteLength !== lock.artifact.bytes ||
+  archiveDigest !== lock.artifact.sha256
+) {
+  throw new Error(
+    `Deterministic reviewed-core archive does not match its locked identity: received ${String(archive.byteLength)} bytes/${archiveDigest}.`
+  );
+}
+
+const artifactDirectory = path.dirname(artifactPath);
+await requireRealDirectory(repositoryRoot);
+await requireRealDirectory(artifactDirectory, true);
+const stagingRoot = await mkdtemp(
+  path.join(artifactDirectory, '.reviewed-core-package-')
+);
+if (
+  !stagingRoot.startsWith(
+    `${path.join(artifactDirectory, '.reviewed-core-package-')}`
+  )
+) {
+  throw new Error(`Unexpected reviewed-core staging path: ${stagingRoot}`);
+}
+try {
+  const stagedArtifact = path.join(stagingRoot, path.basename(artifactPath));
+  await writeFile(stagedArtifact, archive, { flag: 'wx', mode: 0o644 });
+  await rename(stagedArtifact, artifactPath);
+} finally {
+  await rm(stagingRoot, { force: true, recursive: true });
+}
+
+console.log(
+  `Packaged ${lock.assets.length} reviewed FFmpeg assets as ${artifactRelativePath} (${archive.byteLength} bytes, ${archiveDigest})`
+);
--- a/scripts/portal-assembly-smoke.mjs
+++ b/scripts/portal-assembly-smoke.mjs
@@ -16,6 +16,7 @@ const repositoryRoot = path.resolve(
  path.dirname(fileURLToPath(import.meta.url)),
  '..'
 );
+const reviewedCoreBuildId = '0.12.10-reviewed-stack5m.1';

 function consumeValue(argumentsList, index, option) {
  const value = argumentsList[index + 1];
@@ -179,12 +180,21 @@ export function inspectPortalHeaders(configuration) {
      'The config does not explicitly map `.wasm` to application/wasm; verify the pinned image mime.types response.'
    );
  }
-  if (
-    !configuration.includes('vendor/ffmpeg/0\\.12\\.10') &&
-    !configuration.includes('vendor/ffmpeg/0.12.10')
-  ) {
+  const immutableCoreRule = configuration
+    .split(/\r?\n/u)
+    .find(
+      (line) =>
+        /vendor\/ffmpeg\//iu.test(line) &&
+        /ffmpeg-core/iu.test(line) &&
+        /max-age=31536000/iu.test(line) &&
+        /immutable/iu.test(line)
+    );
+  const supportsReviewedCore =
+    immutableCoreRule !== undefined &&
+    immutableCoreRule.replaceAll('\\', '').includes(reviewedCoreBuildId);
+  if (!supportsReviewedCore) {
    warnings.push(
-      'The config does not give versioned FFmpeg core assets an explicit immutable cache rule.'
+      `The config does not give reviewed FFmpeg build ${reviewedCoreBuildId} an explicit immutable cache rule.`
    );
  }
  return { errors, warnings };
@@ -229,11 +239,11 @@ async function verifyAssembly(output, appVersion, digest) {
  }
  for (const reference of [
    './index.html',
-    './vendor/ffmpeg/0.12.10/st/ffmpeg-core.js',
-    './vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm',
-    './vendor/ffmpeg/0.12.10/mt/ffmpeg-core.js',
-    './vendor/ffmpeg/0.12.10/mt/ffmpeg-core.wasm',
-    './vendor/ffmpeg/0.12.10/mt/ffmpeg-core.worker.js',
+    './vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.js',
+    './vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm',
+    './vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.js',
+    './vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.wasm',
+    './vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.worker.js',
  ]) {
    const relative = reference.replace(/^\.\//, '');
    await requireRegularFile(
--- a/scripts/reviewed-ffmpeg-core-lock.json
+++ b/scripts/reviewed-ffmpeg-core-lock.json
@@ -0,0 +1,73 @@
+{
+  "schemaVersion": 1,
+  "buildId": "0.12.10-reviewed-stack5m.1",
+  "profile": "reviewed-stack5m",
+  "coreVersion": "0.12.10",
+  "ffmpegVersion": "n5.1.4",
+  "sourceArchive": {
+    "path": "release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz",
+    "bytes": 43050052,
+    "sha256": "2ab505f72be883d1257bc71cbb93880d1ade5bc029792621cb87b4ecc068399a"
+  },
+  "sourceLock": {
+    "path": "scripts/ffmpeg-source-lock.json",
+    "sha256": "f521ecab59942f899b117e4570bf3a71710fcab6281fe6d796c9bdd22a1fc986"
+  },
+  "buildDriver": {
+    "path": "scripts/build-reviewed-ffmpeg-core.sh",
+    "sha256": "d3551fe12e7883191c41b922850d9bcf7ea093e21ceaa3dec99570db7ea25e2e"
+  },
+  "toolchain": {
+    "emscriptenVersion": "3.1.40",
+    "emscriptenCommit": "5c27e79dd0a9c4e27ef2326841698cdd4f6b5784",
+    "emccSha256": "b0c9551f9155fa9c028efa24591acdfd30f02f32fb247cf9266f5f0f2ede7589",
+    "cmakeVersion": "3.27.9",
+    "cmakeBinarySha256": "ade9326f83f4996b17e2cb1bbfe4848df30a237ef5769cd3c00239b9f0d3ec58"
+  },
+  "patch": {
+    "upstreamCommit": "b409e36475bc21f0451b5b1e1d126fa82871439a",
+    "stackSizeBytes": 5242880,
+    "change": "build/ffmpeg-wasm.sh: add -sSTACK_SIZE=5MB"
+  },
+  "opusRegression": {
+    "fixturePath": "tests/fixtures/generated/tone.wav",
+    "fixtureBytes": 32102,
+    "fixtureSha256": "0fd1f54d6be2f1cc7fd778775dd29cf184770d3716cf3394bf03ed54ac264c3c",
+    "presetId": "audio-opus",
+    "expectedCodec": "opus",
+    "singleThread": true,
+    "multiThread": true
+  },
+  "assets": [
+    {
+      "path": "st/ffmpeg-core.js",
+      "bytes": 111804,
+      "sha256": "80c05d79d0e4e9434977b76cb851d10ddf2bfd378570178700d2c43b8afdcb24"
+    },
+    {
+      "path": "st/ffmpeg-core.wasm",
+      "bytes": 32232580,
+      "sha256": "fe41ddc77220cef6c04f5d48eeffcaaaef179ad270642e098f9945013aa0c9dc"
+    },
+    {
+      "path": "mt/ffmpeg-core.js",
+      "bytes": 128953,
+      "sha256": "4f2650099ab70cb2583951c0421147c62bea6c18dfbba5cfae4d7698b5d0ab62"
+    },
+    {
+      "path": "mt/ffmpeg-core.wasm",
+      "bytes": 32718455,
+      "sha256": "abbead010cb0448b26f01a36a3c8c03a6b04aca07812ddd4719a7f4b6bf4b645"
+    },
+    {
+      "path": "mt/ffmpeg-core.worker.js",
+      "bytes": 2115,
+      "sha256": "f77898d631dc010b45c29c23cb4379c611a7d7b131bf591d08a656bb729a4ca3"
+    }
+  ],
+  "artifact": {
+    "path": "vendor/ffmpeg-core-0.12.10-reviewed-stack5m.1.zip",
+    "bytes": 21338974,
+    "sha256": "ebc068c6d096de55ae3335b04b7121130665f5b0ffa7a828067122733f55185f"
+  }
+}
--- a/scripts/verify-ffmpeg-assets.mjs
+++ b/scripts/verify-ffmpeg-assets.mjs
@@ -1,80 +1,146 @@
 import { createHash } from 'node:crypto';
-import { readFile } from 'node:fs/promises';
-import { dirname, join, relative } from 'node:path';
+import { lstat, readFile } from 'node:fs/promises';
+import path from 'node:path';
 import { fileURLToPath } from 'node:url';
+import { isDeepStrictEqual } from 'node:util';

-const repositoryRoot = join(dirname(fileURLToPath(import.meta.url)), '..');
-const expectedVersion = '0.12.10';
-const outputRoot = join(
+const repositoryRoot = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  '..'
+);
+const argumentsList = process.argv.slice(2);
+const runtimeOnly = argumentsList.includes('--runtime-only');
+if (
+  argumentsList.some((argument) => argument !== '--runtime-only') ||
+  (runtimeOnly && argumentsList.length !== 1)
+) {
+  throw new Error(
+    'Usage: node scripts/verify-ffmpeg-assets.mjs [--runtime-only]'
+  );
+}
+const lock = JSON.parse(
+  await readFile(
+    path.join(repositoryRoot, 'scripts', 'reviewed-ffmpeg-core-lock.json'),
+    'utf8'
+  )
+);
+if (
+  lock.schemaVersion !== 1 ||
+  typeof lock.buildId !== 'string' ||
+  !/^[a-zA-Z0-9._-]+$/.test(lock.buildId) ||
+  lock.coreVersion !== '0.12.10' ||
+  lock.profile !== 'reviewed-stack5m' ||
+  lock.sourceArchive?.path !==
+    'release/ffmpeg-core-0.12.10-reviewed-stack5m.1-corresponding-source.tar.xz' ||
+  !Number.isSafeInteger(lock.sourceArchive?.bytes) ||
+  lock.sourceArchive.bytes < 1 ||
+  lock.sourceArchive.bytes > 512 * 1024 * 1024 ||
+  !/^[a-f0-9]{64}$/.test(lock.sourceArchive?.sha256 ?? '') ||
+  lock.sourceLock?.path !== 'scripts/ffmpeg-source-lock.json' ||
+  !/^[a-f0-9]{64}$/.test(lock.sourceLock?.sha256 ?? '') ||
+  lock.buildDriver?.path !== 'scripts/build-reviewed-ffmpeg-core.sh' ||
+  !/^[a-f0-9]{64}$/.test(lock.buildDriver?.sha256 ?? '') ||
+  lock.artifact?.path !== `vendor/ffmpeg-core-${lock.buildId}.zip` ||
+  !Number.isSafeInteger(lock.artifact?.bytes) ||
+  lock.artifact.bytes < 1 ||
+  lock.artifact.bytes > 64 * 1024 * 1024 ||
+  !/^[a-f0-9]{64}$/.test(lock.artifact?.sha256 ?? '') ||
+  !Array.isArray(lock.assets) ||
+  lock.assets.length !== 5
+) {
+  throw new Error('Invalid reviewed FFmpeg core lock.');
+}
+const outputRoot = path.join(
  repositoryRoot,
  'public',
  'vendor',
  'ffmpeg',
-  expectedVersion
+  lock.buildId
 );
-const manifestPath = join(outputRoot, 'version.json');
+const manifestPath = path.join(outputRoot, 'version.json');
 const manifest = JSON.parse(await readFile(manifestPath, 'utf8'));
+const sha256 = (bytes) => createHash('sha256').update(bytes).digest('hex');
+const safeAssetPath = (value) => {
+  if (
+    typeof value !== 'string' ||
+    value.length === 0 ||
+    value.includes('\\') ||
+    value.includes('\0') ||
+    value.startsWith('/') ||
+    path.posix.normalize(value) !== value ||
+    value.split('/').some((part) => !part || part === '.' || part === '..')
+  ) {
+    throw new Error(`Unsafe FFmpeg asset path: ${String(value)}`);
+  }
+  return value;
+};
+
+const verifyLockedFile = async (record, label) => {
+  const relative = safeAssetPath(record.path);
+  const absolute = path.join(repositoryRoot, ...relative.split('/'));
+  const details = await lstat(absolute).catch((error) => {
+    throw new Error(`${label} is missing: ${relative}`, { cause: error });
+  });
+  if (details.isSymbolicLink() || !details.isFile()) {
+    throw new Error(`${label} must be a regular file: ${relative}`);
+  }
+  const bytes = await readFile(absolute);
+  if (
+    (record.bytes !== undefined && bytes.byteLength !== record.bytes) ||
+    sha256(bytes) !== record.sha256
+  ) {
+    throw new Error(`${label} does not match its locked identity: ${relative}`);
+  }
+};

 if (
-  manifest.schemaVersion !== 1 ||
-  manifest.coreVersion !== expectedVersion ||
+  manifest.schemaVersion !== 2 ||
+  manifest.buildId !== lock.buildId ||
+  manifest.profile !== lock.profile ||
+  manifest.coreVersion !== lock.coreVersion ||
+  manifest.ffmpegVersion !== lock.ffmpegVersion ||
+  !isDeepStrictEqual(manifest.sourceArchive, lock.sourceArchive) ||
+  !isDeepStrictEqual(manifest.sourceLock, lock.sourceLock) ||
+  !isDeepStrictEqual(manifest.buildDriver, lock.buildDriver) ||
+  !isDeepStrictEqual(manifest.toolchain, lock.toolchain) ||
+  !isDeepStrictEqual(manifest.patch, lock.patch) ||
+  !isDeepStrictEqual(manifest.opusRegression, lock.opusRegression) ||
  !Array.isArray(manifest.assets) ||
-  manifest.assets.length !== 5
+  manifest.assets.length !== lock.assets.length
 ) {
-  throw new Error(`Invalid FFmpeg asset manifest: ${manifestPath}`);
+  throw new Error(`Invalid reviewed FFmpeg asset manifest: ${manifestPath}`);
 }

-const expectedPaths = new Set([
-  'mt/ffmpeg-core.js',
-  'mt/ffmpeg-core.wasm',
-  'mt/ffmpeg-core.worker.js',
-  'st/ffmpeg-core.js',
-  'st/ffmpeg-core.wasm',
-]);
-const expectedHashes = new Map([
-  [
-    'st/ffmpeg-core.js',
-    '67a48f11645f85439f3fde4f2119042c16b374b910206b7a7a24f342e28dcae3',
-  ],
-  [
-    'st/ffmpeg-core.wasm',
-    '9f57947a5bd530d8f00c5b3f2cb2a3492faa7e5d823315342d6a8656d0a6b7b7',
-  ],
-  [
-    'mt/ffmpeg-core.js',
-    '270a2e6ff945e173238610669a3f7132df5f9c52698a9bf708cf5c2ab6bda0de',
-  ],
-  [
-    'mt/ffmpeg-core.wasm',
-    'be2c97605366b78f3f13e21b52e81a55a79e1f29c133b03a68ec187b1a2ec41a',
-  ],
-  [
-    'mt/ffmpeg-core.worker.js',
-    'f77898d631dc010b45c29c23cb4379c611a7d7b131bf591d08a656bb729a4ca3',
-  ],
-]);
+if (!runtimeOnly) {
+  await verifyLockedFile(lock.sourceArchive, 'FFmpeg Corresponding Source');
+}
+await verifyLockedFile(lock.sourceLock, 'FFmpeg source lock');
+await verifyLockedFile(lock.buildDriver, 'Reviewed-core build driver');
+await verifyLockedFile(lock.artifact, 'Reviewed-core deterministic artifact');

+const lockedAssets = new Map(lock.assets.map((asset) => [asset.path, asset]));
+const seen = new Set();
 for (const asset of manifest.assets) {
-  if (!expectedPaths.delete(asset.path)) {
-    throw new Error(`Unexpected or duplicate FFmpeg asset: ${asset.path}`);
-  }
-  const bytes = await readFile(join(outputRoot, asset.path));
-  const digest = createHash('sha256').update(bytes).digest('hex');
+  safeAssetPath(asset.path);
+  const locked = lockedAssets.get(asset.path);
  if (
-    asset.bytes !== bytes.byteLength ||
-    asset.sha256 !== digest ||
-    expectedHashes.get(asset.path) !== digest
+    !locked ||
+    seen.has(asset.path) ||
+    asset.bytes !== locked.bytes ||
+    asset.sha256 !== locked.sha256
  ) {
+    throw new Error(`Unexpected reviewed FFmpeg asset: ${asset.path}`);
+  }
+  seen.add(asset.path);
+  const bytes = await readFile(path.join(outputRoot, ...asset.path.split('/')));
+  if (bytes.byteLength !== locked.bytes || sha256(bytes) !== locked.sha256) {
    throw new Error(`FFmpeg asset verification failed: ${asset.path}`);
  }
 }
-
-if (expectedPaths.size > 0) {
-  throw new Error(
-    `FFmpeg assets are missing: ${[...expectedPaths].join(', ')}`
-  );
+if (seen.size !== lockedAssets.size) {
+  throw new Error('One or more reviewed FFmpeg assets are missing.');
 }

 console.log(
-  `Verified 5 FFmpeg ${expectedVersion} assets in ${relative(repositoryRoot, outputRoot)}`
+  `Verified ${seen.size} FFmpeg ${lock.buildId} assets in ${path.relative(repositoryRoot, outputRoot)}${runtimeOnly ? ' (runtime inputs only)' : ' with Corresponding Source'}`
 );
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -9,6 +9,10 @@ import {
  type WorkspaceMode,
 } from './app/application-state';
 import { AppErrorBoundary } from './app/AppErrorBoundary';
+import {
+  SourceInspectionRegistry,
+  type SourceInspectionToken,
+} from './app/source-inspection-registry';
 import { FileDropZone } from './components/FileDropZone';
 import { MediaBin } from './components/MediaBin';
 import {
@@ -79,7 +83,10 @@ import { buildPreviewProxyPlan } from './commands/preview-proxy';
 import { buildTimelineExportPlan } from './commands/timeline-export';
 import {
  buildContactSheetPlan,
+  buildSceneChangeAnalysisPlan,
+  buildSceneThumbnailSeriesPlan,
  buildThumbnailSeriesPlan,
+  parseSceneChangeFrames,
 } from './commands/thumbnails';
 import { buildSplitPlan } from './commands/split';
 import { buildTrimPlan } from './commands/trim';
@@ -152,6 +159,11 @@ import {
  type WaveformPeakData,
 } from './waveform';
 import type { MediaJob, MediaJobStep } from './jobs';
+import { loadBundledContactSheetFont } from './assets/bundled-font';
+import {
+  FFMPEG_CORE_VERSION,
+  FFMPEG_OPUS_REGRESSION_VERIFIED,
+} from './version';

 function timestamp(): string {
  return new Date().toISOString();
@@ -554,6 +566,7 @@ export function AvToolsApplication() {
  const projectRef = useRef(project);
  const sourceProbeTail = useRef<Promise<void>>(Promise.resolve());
  const sourceProbePendingRef = useRef(0);
+  const sourceInspectionRegistry = useRef(new SourceInspectionRegistry());
  const planExecutionTail = useRef<Promise<void>>(Promise.resolve());
  const scheduledPlanCountRef = useRef(0);
  const scheduledWorkRef = useRef(new Map<string, ScheduledWorkDefinition>());
@@ -703,7 +716,10 @@ export function AvToolsApplication() {
  );

  useEffect(() => {
+    const inspectionRegistry = sourceInspectionRegistry.current;
    return () => {
+      const cancelActiveInspection = inspectionRegistry.clear();
+      if (cancelActiveInspection) void engineManager.cancelActive();
      for (const asset of assetsRef.current) {
        URL.revokeObjectURL(asset.objectUrl);
      }
@@ -751,15 +767,37 @@ export function AvToolsApplication() {
  );

  const inspectAsset = useCallback(
-    async (asset: ImportedMediaAsset, existingAsset: boolean) => {
+    async (
+      asset: ImportedMediaAsset,
+      existingAsset: boolean,
+      token: SourceInspectionToken
+    ) => {
+      if (!sourceInspectionRegistry.current.isCurrent(token)) return;
      updateAssetState(asset.id, {
        phase: 'probing',
        error: undefined,
      });
      try {
-        const probeResult = await runSourceProbe(() =>
-          engineManager.probe(asset.file)
+        const probeResult = await runSourceProbe(async () => {
+          if (!sourceInspectionRegistry.current.activate(token)) {
+            return undefined;
+          }
+          try {
+            return await engineManager.probe(
+              asset.file,
+              undefined,
+              token.signal
            );
+          } finally {
+            sourceInspectionRegistry.current.finish(token);
+          }
+        });
+        if (
+          !probeResult ||
+          !sourceInspectionRegistry.current.isCurrent(token)
+        ) {
+          return;
+        }
        const probe = normalizeFfprobeReport(probeResult.json);
        const rawProbe = `${JSON.stringify(probeResult.json, null, 2)}\n`;
        const importedChapters = probe.chapters.map((chapter) => ({
@@ -772,8 +810,15 @@ export function AvToolsApplication() {
            ? { metadata: chapter.tags }
            : {}),
        }));
+        if (!sourceInspectionRegistry.current.isCurrent(token)) return;
        updateAssetState(asset.id, { phase: 'ready', probe, rawProbe });
        setProject((current) => {
+          if (
+            !sourceInspectionRegistry.current.isCurrent(token) ||
+            !current.assets.some((entry) => entry.id === asset.id)
+          ) {
+            return current;
+          }
          let next = projectReducer(current, {
            type: 'asset/update',
            assetId: asset.id,
@@ -823,6 +868,7 @@ export function AvToolsApplication() {
          return next;
        });
      } catch (error) {
+        if (!sourceInspectionRegistry.current.isCurrent(token)) return;
        updateAssetState(asset.id, {
          phase: 'error',
          error:
@@ -881,6 +927,7 @@ export function AvToolsApplication() {
      const pending: Array<{
        asset: ImportedMediaAsset;
        existingAsset: boolean;
+        token: SourceInspectionToken;
      }> = [];
      const claimedIds = new Set(assetsRef.current.map((asset) => asset.id));

@@ -916,7 +963,11 @@ export function AvToolsApplication() {
        if (reattach && match) {
          asset.id = match.entry.id;
          claimedIds.add(match.entry.id);
-          pending.push({ asset, existingAsset: true });
+          pending.push({
+            asset,
+            existingAsset: true,
+            token: sourceInspectionRegistry.current.register(asset.id),
+          });
        } else {
          setProject((current) =>
            projectReducer(current, {
@@ -932,7 +983,11 @@ export function AvToolsApplication() {
              updatedAt: timestamp(),
            })
          );
-          pending.push({ asset, existingAsset: false });
+          pending.push({
+            asset,
+            existingAsset: false,
+            token: sourceInspectionRegistry.current.register(asset.id),
+          });
        }
      }

@@ -943,7 +998,7 @@ export function AvToolsApplication() {
      });
      setSelectedAssetId((current) => current ?? pending[0]?.asset.id);
      for (const item of pending) {
-        await inspectAsset(item.asset, item.existingAsset);
+        await inspectAsset(item.asset, item.existingAsset, item.token);
      }
    },
    [inspectAsset, project.assets, resourceContext.policy]
@@ -953,7 +1008,13 @@ export function AvToolsApplication() {
    (id: string) => {
      const asset = assets.find((entry) => entry.id === id);
      if (asset) URL.revokeObjectURL(asset.objectUrl);
-      setAssets((current) => current.filter((entry) => entry.id !== id));
+      const cancelActiveInspection =
+        sourceInspectionRegistry.current.remove(id);
+      setAssets((current) => {
+        const next = current.filter((entry) => entry.id !== id);
+        assetsRef.current = next;
+        return next;
+      });
      setWaveformByAsset((current) =>
        Object.fromEntries(
          Object.entries(current).filter(([assetId]) => assetId !== id)
@@ -982,6 +1043,7 @@ export function AvToolsApplication() {
        assetId: id,
        updatedAt: timestamp(),
      });
+      if (cancelActiveInspection) void engineManager.cancelActive();
    },
    [applyProjectAction, assets, selectedAssetId]
  );
@@ -1203,7 +1265,7 @@ export function AvToolsApplication() {
                    ? ('multi-thread' as const)
                    : ('single-thread' as const),
                ffmpegVersion: readyStateAfterRun.capabilities.versionText,
-                coreVersion: '0.12.10',
+                coreVersion: FFMPEG_CORE_VERSION,
              }
            : {}),
        },
@@ -2245,6 +2307,9 @@ export function AvToolsApplication() {

  const resetProject = useCallback(() => {
    for (const asset of assets) URL.revokeObjectURL(asset.objectUrl);
+    const cancelActiveInspection = sourceInspectionRegistry.current.clear();
+    if (cancelActiveInspection) void engineManager.cancelActive();
+    assetsRef.current = [];
    clearResult();
    setAssets([]);
    setSelectedAssetId(undefined);
@@ -2280,6 +2345,9 @@ export function AvToolsApplication() {
      try {
        const imported = importProjectDocument(await file.text());
        for (const asset of assets) URL.revokeObjectURL(asset.objectUrl);
+        const cancelActiveInspection = sourceInspectionRegistry.current.clear();
+        if (cancelActiveInspection) void engineManager.cancelActive();
+        assetsRef.current = [];
        clearResult();
        setAssets([]);
        setSelectedAssetId(undefined);
@@ -2556,6 +2624,7 @@ export function AvToolsApplication() {
                channelLayout: 'stereo',
                missingAudioPolicy: request.missingAudioPolicy,
                subtitlePolicy: request.subtitlePolicy,
+                crossfadeSeconds: request.crossfadeSeconds,
              });
            })();
      await runPlan(
@@ -2950,30 +3019,77 @@ export function AvToolsApplication() {
      if (!asset || duration === undefined) {
        throw new Error('Select an attached, inspected video source first.');
      }
-      const distribution =
-        request.distribution.type === 'evenly-spaced'
-          ? { count: request.distribution.count }
-          : request.distribution.type === 'fixed-interval'
-            ? { intervalSeconds: request.distribution.intervalSeconds }
-            : { timesSeconds: request.distribution.timesSeconds };
-      const plan = buildThumbnailSeriesPlan({
-        jobId: crypto.randomUUID(),
-        source: {
+      const source = {
        id: asset.id,
        sourceIndex: 0,
        fileName: asset.file.name,
-        },
-        durationSeconds: duration,
-        ...distribution,
-        size: {
+      };
+      const size = {
        ...(request.width ? { width: request.width } : {}),
        ...(request.height ? { height: request.height } : {}),
-        },
+      };
+      const sceneDistribution =
+        request.distribution.type === 'scene-changes'
+          ? request.distribution
+          : undefined;
+      const execution = sceneDistribution
+        ? await runWorkflow(
+            'Create scene-change thumbnails',
+            2,
+            async (executeStep) => {
+              const analysis = await executeStep(
+                buildSceneChangeAnalysisPlan({
+                  jobId: crypto.randomUUID(),
+                  source,
+                  durationSeconds: duration,
+                  threshold: sceneDistribution.threshold,
+                  maxFrames: sceneDistribution.count,
+                }),
+                [asset.file],
+                'Analyze scene changes'
+              );
+              const frames = parseSceneChangeFrames(analysis.logText).slice(
+                0,
+                sceneDistribution.count
+              );
+              if (frames.length === 0) {
+                throw new Error(
+                  'No scene changes met this threshold. Lower the threshold or use evenly spaced frames.'
+                );
+              }
+              return executeStep(
+                buildSceneThumbnailSeriesPlan({
+                  jobId: crypto.randomUUID(),
+                  source,
+                  durationSeconds: duration,
+                  frames,
+                  size,
                  format: request.format,
                  quality: request.quality,
-      });
-      const execution = await runPlan(
-        plan,
+                }),
+                [asset.file],
+                'Extract analyzed scene frames'
+              );
+            }
+          )
+        : await runPlan(
+            buildThumbnailSeriesPlan({
+              jobId: crypto.randomUUID(),
+              source,
+              durationSeconds: duration,
+              ...(request.distribution.type === 'evenly-spaced'
+                ? { count: request.distribution.count }
+                : request.distribution.type === 'fixed-interval'
+                  ? {
+                      intervalSeconds: request.distribution.intervalSeconds,
+                    }
+                  : request.distribution.type === 'scene-changes'
+                    ? { count: request.distribution.count }
+                    : { timesSeconds: request.distribution.timesSeconds }),
+              size,
+              format: request.format,
+              quality: request.quality,
+            }),
            [asset.file],
            'Create thumbnail series'
          );
@@ -3002,7 +3118,7 @@ export function AvToolsApplication() {
        );
      }
    },
-    [inspectedClipAsset, project.id, runPlan]
+    [inspectedClipAsset, project.id, runPlan, runWorkflow]
  );

  const handleContactSheet = useCallback(
@@ -3012,22 +3128,75 @@ export function AvToolsApplication() {
      if (!asset || duration === undefined) {
        throw new Error('Select an attached, inspected video source first.');
      }
-      const plan = buildContactSheetPlan({
-        jobId: crypto.randomUUID(),
-        source: {
+      const source = {
        id: asset.id,
        sourceIndex: 0,
        fileName: asset.file.name,
-        },
+      };
+      const labelsRequested = request.timestampLabels || request.sourceLabel;
+      const font = labelsRequested
+        ? await loadBundledContactSheetFont()
+        : undefined;
+      const buildSheet = (
+        sceneFrames?: ReturnType<typeof parseSceneChangeFrames>
+      ) =>
+        buildContactSheetPlan({
+          jobId: crypto.randomUUID(),
+          source,
          durationSeconds: duration,
          ...request,
-        drawtextAvailable: false,
+          ...(sceneFrames
+            ? { frameCount: sceneFrames.length, sceneFrames }
+            : {}),
+          drawtextAvailable: Boolean(font),
+          ...(font
+            ? {
+                font: {
+                  id: 'bundled-contact-sheet-font',
+                  sourceIndex: 1,
+                  fileName: font.name,
+                },
+              }
+            : {}),
        });
-      const execution = await runPlan(
-        plan,
+      const inputs = font ? [asset.file, font] : [asset.file];
+      const sceneSelection =
+        request.selection.type === 'scene-changes'
+          ? request.selection
+          : undefined;
+      const execution = sceneSelection
+        ? await runWorkflow(
+            'Create scene-change contact sheet',
+            2,
+            async (executeStep) => {
+              const analysis = await executeStep(
+                buildSceneChangeAnalysisPlan({
+                  jobId: crypto.randomUUID(),
+                  source,
+                  durationSeconds: duration,
+                  threshold: sceneSelection.threshold,
+                  maxFrames: request.frameCount,
+                }),
                [asset.file],
-        'Create contact sheet'
+                'Analyze scene changes'
              );
+              const frames = parseSceneChangeFrames(analysis.logText).slice(
+                0,
+                request.frameCount
+              );
+              if (frames.length === 0) {
+                throw new Error(
+                  'No scene changes met this threshold. Lower the threshold or use evenly spaced frames.'
+                );
+              }
+              return executeStep(
+                buildSheet(frames),
+                inputs,
+                'Render scene-change contact sheet'
+              );
+            }
+          )
+        : await runPlan(buildSheet(), inputs, 'Create contact sheet');
      const output = execution.results[0];
      if (!output) throw new Error('The contact sheet was not returned.');
      try {
@@ -3045,7 +3214,7 @@ export function AvToolsApplication() {
        );
      }
    },
-    [inspectedClipAsset, project.id, runPlan]
+    [inspectedClipAsset, project.id, runPlan, runWorkflow]
  );

  const handleMetadataAction = useCallback(
@@ -3413,7 +3582,8 @@ export function AvToolsApplication() {
          status: 'unavailable' as const,
          reasons: ['Initialize the engine to verify this preset.'],
        };
-    const opusBlocked = preset.audio?.codec === 'libopus';
+    const opusBlocked =
+      preset.audio?.codec === 'libopus' && !FFMPEG_OPUS_REGRESSION_VERIFIED;
    return {
      id: preset.id,
      name: preset.name,
@@ -3423,7 +3593,7 @@ export function AvToolsApplication() {
      ...(availability.status === 'unavailable' || opusBlocked
        ? {
            disabledReason: opusBlocked
-              ? 'Opus output remains disabled until the pinned core passes its non-empty ST/MT regression smoke.'
+              ? 'Opus output is disabled until the reviewed core passes the non-empty ST/MT regression encode and re-probe gate.'
              : availability.reasons.join(' '),
          }
        : {}),
@@ -3481,6 +3651,7 @@ export function AvToolsApplication() {
          hasAudio: false,
          hasVideo: false,
          hasSubtitles: false,
+          durationSeconds: clip.sourceOutSeconds - clip.sourceInSeconds,
        };
      }
      const unsupportedStreams = asset.probe.streams.filter(
@@ -3517,6 +3688,7 @@ export function AvToolsApplication() {
      return {
        id: clip.id,
        label,
+        durationSeconds: clip.sourceOutSeconds - clip.sourceInSeconds,
        hasAudio: asset.probe.streams.some((stream) => stream.type === 'audio'),
        hasVideo: asset.probe.streams.some(
          (stream) =>
@@ -3622,10 +3794,12 @@ export function AvToolsApplication() {
      filters: ['fps', 'scale', 'tile'],
    }),
    'contact-sheet-labels': {
-      available: false,
-      reason:
-        'No reviewed local font is bundled, so labels are omitted instead of fetching a remote font.',
+      ...capabilityStatus({ filters: ['drawtext'] }),
    },
+    'scene-change-analysis': capabilityStatus({
+      muxers: ['null'],
+      filters: ['select', 'showinfo'],
+    }),
    'metadata-write': sourceMuxer
      ? capabilityStatus({ muxers: [sourceMuxer] })
      : { available: false, reason: 'Select a source first.' },
@@ -3678,6 +3852,9 @@ export function AvToolsApplication() {
      },
      anyVideoPreset ? undefined : 'No verified video preset is available.'
    ),
+    'concat-crossfade': capabilityStatus({
+      filters: ['xfade', ...(structuralHasAnyAudio ? ['acrossfade'] : [])],
+    }),
  } as const;

  const advancedSource = inspectedClipAsset?.probe
--- a/src/app/source-inspection-registry.ts
+++ b/src/app/source-inspection-registry.ts
@@ -0,0 +1,76 @@
+export interface SourceInspectionToken {
+  readonly assetId: string;
+  readonly generation: number;
+  readonly signal: AbortSignal;
+}
+
+/**
+ * Tracks the exact runtime import that owns queued or active inspection work.
+ *
+ * Project asset IDs can be reused when a missing source is reattached, so an
+ * ID-only check is insufficient: a late result from the old File must not be
+ * applied to the replacement. Tokens are intentionally kept outside React
+ * state so removal invalidates work synchronously.
+ */
+export class SourceInspectionRegistry {
+  readonly #currentByAsset = new Map<
+    string,
+    { readonly generation: number; readonly controller: AbortController }
+  >();
+  #nextGeneration = 0;
+  #activeToken: SourceInspectionToken | undefined;
+
+  register(assetId: string): SourceInspectionToken {
+    const controller = new AbortController();
+    const token = Object.freeze({
+      assetId,
+      generation: ++this.#nextGeneration,
+      signal: controller.signal,
+    });
+    this.#currentByAsset.get(assetId)?.controller.abort();
+    this.#currentByAsset.set(assetId, {
+      generation: token.generation,
+      controller,
+    });
+    return token;
+  }
+
+  isCurrent(token: SourceInspectionToken): boolean {
+    return (
+      this.#currentByAsset.get(token.assetId)?.generation === token.generation
+    );
+  }
+
+  activate(token: SourceInspectionToken): boolean {
+    if (!this.isCurrent(token)) return false;
+    this.#activeToken = token;
+    return true;
+  }
+
+  finish(token: SourceInspectionToken): void {
+    if (
+      this.#activeToken?.assetId === token.assetId &&
+      this.#activeToken.generation === token.generation
+    ) {
+      this.#activeToken = undefined;
+    }
+  }
+
+  remove(assetId: string): boolean {
+    const current = this.#currentByAsset.get(assetId);
+    current?.controller.abort();
+    this.#currentByAsset.delete(assetId);
+    return (
+      this.#activeToken?.assetId === assetId &&
+      this.#activeToken.generation === current?.generation
+    );
+  }
+
+  clear(): boolean {
+    for (const current of this.#currentByAsset.values()) {
+      current.controller.abort();
+    }
+    this.#currentByAsset.clear();
+    return this.#activeToken !== undefined;
+  }
+}
--- a/src/assets/bundled-font.ts
+++ b/src/assets/bundled-font.ts
@@ -0,0 +1,54 @@
+export const BUNDLED_CONTACT_SHEET_FONT = Object.freeze({
+  family: 'DejaVu Sans',
+  fileName: 'DejaVuSans.ttf',
+  byteLength: 757_076,
+  sha256: '7da195a74c55bef988d0d48f9508bd5d849425c1770dba5d7bfc6ce9ed848954',
+  licenseFile: 'LICENSES/DEJAVU_FONTS.txt',
+});
+
+let fontPromise: Promise<File> | undefined;
+
+/**
+ * Loads the same-origin reviewed font and verifies its release identity before
+ * it is mounted read-only for FFmpeg. A failed check is never silently replaced
+ * with a system or remote font.
+ */
+export function loadBundledContactSheetFont(): Promise<File> {
+  fontPromise ??= loadAndVerifyFont().catch((error: unknown) => {
+    fontPromise = undefined;
+    throw error;
+  });
+  return fontPromise;
+}
+
+async function loadAndVerifyFont(): Promise<File> {
+  const response = await fetch(
+    `${import.meta.env.BASE_URL}fonts/${BUNDLED_CONTACT_SHEET_FONT.fileName}`,
+    {
+      cache: 'force-cache',
+      credentials: 'same-origin',
+    }
+  );
+  if (!response.ok) {
+    throw new Error(
+      `The bundled contact-sheet font could not be loaded (${response.status}).`
+    );
+  }
+  const bytes = new Uint8Array(await response.arrayBuffer());
+  if (bytes.byteLength !== BUNDLED_CONTACT_SHEET_FONT.byteLength) {
+    throw new Error('The bundled contact-sheet font has an unexpected size.');
+  }
+  const digest = await crypto.subtle.digest('SHA-256', bytes);
+  const sha256 = [...new Uint8Array(digest)]
+    .map((value) => value.toString(16).padStart(2, '0'))
+    .join('');
+  if (sha256 !== BUNDLED_CONTACT_SHEET_FONT.sha256) {
+    throw new Error(
+      'The bundled contact-sheet font failed its SHA-256 identity check.'
+    );
+  }
+  return new File([bytes], BUNDLED_CONTACT_SHEET_FONT.fileName, {
+    type: 'font/ttf',
+    lastModified: 0,
+  });
+}
--- a/src/commands/concatenate.ts
+++ b/src/commands/concatenate.ts
@@ -42,6 +42,8 @@ export interface ConcatSource extends SourceReference {

 export type MissingAudioPolicy = 'insert-silence' | 'drop-all' | 'reject';
 const MAX_CONCAT_SOURCES = 100;
+export const MIN_CROSSFADE_SECONDS = 0.04;
+export const MAX_CROSSFADE_SECONDS = 10;

 export interface FastConcatOptions {
  readonly jobId: string;
@@ -59,6 +61,11 @@ export interface NormalizedConcatOptions extends FastConcatOptions {
  readonly channelLayout?: 'mono' | 'stereo' | '5.1';
  readonly missingAudioPolicy: MissingAudioPolicy;
  readonly subtitlePolicy?: 'drop-all' | 'reject';
+  /**
+   * Uniform overlap at every edit. Zero/undefined keeps hard cuts. The command
+   * layer bounds both the transition and the available material around edits.
+   */
+  readonly crossfadeSeconds?: number;
 }

 export function validateConcatCompatibility(
@@ -334,6 +341,8 @@ export function buildNormalizedConcatPlan(
  }
  const includeAudio =
    options.missingAudioPolicy !== 'drop-all' && hasAudio.some(Boolean);
+  const crossfadeSeconds = options.crossfadeSeconds ?? 0;
+  validateCrossfade(crossfadeSeconds, ranges);
  const inputs = options.sources.map((source) =>
    createPlannedInput(options.jobId, source)
  );
@@ -360,12 +369,35 @@ export function buildNormalizedConcatPlan(
      }
    }
  });
+  if (crossfadeSeconds > 0) {
+    let videoLabel = 'v0';
+    let audioLabel = 'a0';
+    let effectiveDuration = ranges[0]?.durationSeconds ?? 0;
+    for (let index = 1; index < options.sources.length; index += 1) {
+      const finalTransition = index === options.sources.length - 1;
+      const nextVideoLabel = finalTransition ? 'vout' : `vxf${index}`;
+      graphParts.push(
+        `[${videoLabel}][v${index}]xfade=transition=fade:duration=${normalizeSeconds(crossfadeSeconds)}:offset=${normalizeSeconds(effectiveDuration - crossfadeSeconds)}[${nextVideoLabel}]`
+      );
+      videoLabel = nextVideoLabel;
+      if (includeAudio) {
+        const nextAudioLabel = finalTransition ? 'aout' : `axf${index}`;
+        graphParts.push(
+          `[${audioLabel}][a${index}]acrossfade=d=${normalizeSeconds(crossfadeSeconds)}:c1=tri:c2=tri[${nextAudioLabel}]`
+        );
+        audioLabel = nextAudioLabel;
+      }
+      effectiveDuration +=
+        (ranges[index]?.durationSeconds ?? 0) - crossfadeSeconds;
+    }
+  } else {
    const labels = options.sources
      .map((_, index) => `[v${index}]${includeAudio ? `[a${index}]` : ''}`)
      .join('');
    graphParts.push(
      `${labels}concat=n=${options.sources.length}:v=1:a=${includeAudio ? 1 : 0}[vout]${includeAudio ? '[aout]' : ''}`
    );
+  }
  args.push('-filter_complex', graphParts.join(';'), '-map', '[vout]');
  if (includeAudio) {
    args.push('-map', '[aout]');
@@ -397,10 +429,9 @@ export function buildNormalizedConcatPlan(
    temporaryFiles: [],
    args,
    outputs: [output],
-    expectedDurationSeconds: ranges.reduce(
-      (sum, range) => sum + range.durationSeconds,
-      0
-    ),
+    expectedDurationSeconds:
+      ranges.reduce((sum, range) => sum + range.durationSeconds, 0) -
+      crossfadeSeconds * (ranges.length - 1),
    requiredCapabilities: mergeRequirements(presetRequirements, {
      muxers: [options.targetMuxer],
      filters: [
@@ -411,7 +442,8 @@ export function buildNormalizedConcatPlan(
        'setsar',
        'fps',
        'format',
-        'concat',
+        ...(crossfadeSeconds > 0 ? ['xfade'] : ['concat']),
+        ...(crossfadeSeconds > 0 && includeAudio ? ['acrossfade'] : []),
        ...(includeAudio ? ['atrim', 'asetpts', 'aresample', 'aformat'] : []),
        ...(mixedAudioPresence &&
        options.missingAudioPolicy === 'insert-silence'
@@ -423,7 +455,9 @@ export function buildNormalizedConcatPlan(
      diagnostic(
        'normalized-concat',
        'info',
-        'Clips are normalized to common video and audio properties, then re-encoded.'
+        crossfadeSeconds > 0
+          ? `Clips are normalized and joined with a ${normalizeSeconds(crossfadeSeconds)} second audio/video crossfade at every edit.`
+          : 'Clips are normalized to common video and audio properties, then re-encoded.'
      ),
      ...(mixedAudioPresence && options.missingAudioPolicy === 'insert-silence'
        ? [
@@ -447,6 +481,34 @@ export function buildNormalizedConcatPlan(
  });
 }

+function validateCrossfade(
+  crossfadeSeconds: number,
+  ranges: readonly { readonly durationSeconds: number }[]
+): void {
+  if (!Number.isFinite(crossfadeSeconds) || crossfadeSeconds < 0) {
+    throw new RangeError('Crossfade duration must be finite and nonnegative');
+  }
+  if (crossfadeSeconds === 0) {
+    return;
+  }
+  if (
+    crossfadeSeconds < MIN_CROSSFADE_SECONDS ||
+    crossfadeSeconds > MAX_CROSSFADE_SECONDS
+  ) {
+    throw new RangeError(
+      `Crossfade duration must be ${MIN_CROSSFADE_SECONDS}–${MAX_CROSSFADE_SECONDS} seconds`
+    );
+  }
+  for (const [index, range] of ranges.entries()) {
+    const required = index === 0 || index === ranges.length - 1 ? 1 : 2;
+    if (range.durationSeconds < crossfadeSeconds * required) {
+      throw new RangeError(
+        `Clip ${index + 1} needs at least ${normalizeSeconds(crossfadeSeconds * required)} seconds for the requested crossfade material`
+      );
+    }
+  }
+}
+
 function comparableKeys(
  kind: ConcatStreamDescription['kind']
 ): readonly (keyof ConcatStreamDescription)[] {
--- a/src/commands/thumbnails.ts
+++ b/src/commands/thumbnails.ts
@@ -14,6 +14,16 @@ import { freezeCommandPlan, type FFmpegCommandPlan } from './command-plan';

 export type ImageFormat = 'png' | 'jpeg' | 'webp';

+export const MAX_SCENE_CHANGE_FRAMES = 100;
+export const MIN_SCENE_CHANGE_THRESHOLD = 0.01;
+export const MAX_SCENE_CHANGE_THRESHOLD = 0.95;
+
+export interface SceneChangeFrame {
+  /** Exact source presentation timestamp in the source video time base. */
+  readonly pts: number;
+  readonly timeSeconds: number;
+}
+
 export interface ThumbnailSize {
  readonly width?: number;
  readonly height?: number;
@@ -41,6 +51,21 @@ export interface ThumbnailSeriesOptions {
  readonly quality?: number;
 }

+export interface SceneChangeAnalysisOptions {
+  readonly jobId: string;
+  readonly source: SourceReference;
+  readonly durationSeconds: number;
+  readonly threshold: number;
+  readonly maxFrames: number;
+}
+
+export interface SceneThumbnailSeriesOptions extends Omit<
+  ThumbnailSeriesOptions,
+  'timesSeconds' | 'intervalSeconds' | 'count'
+> {
+  readonly frames: readonly SceneChangeFrame[];
+}
+
 export interface ContactSheetOptions {
  readonly jobId: string;
  readonly source: SourceReference;
@@ -57,6 +82,10 @@ export interface ContactSheetOptions {
  readonly format: ImageFormat;
  readonly quality?: number;
  readonly drawtextAvailable?: boolean;
+  /** Reviewed local font mounted as a second, read-only job input. */
+  readonly font?: SourceReference;
+  /** Exact frames returned by a preceding bounded scene-change analysis. */
+  readonly sceneFrames?: readonly SceneChangeFrame[];
 }

 export function buildSingleThumbnailPlan(
@@ -164,6 +193,148 @@ export function buildThumbnailSeriesPlan(
  });
 }

+export function buildSceneChangeAnalysisPlan(
+  options: SceneChangeAnalysisOptions
+): FFmpegCommandPlan {
+  validateSceneAnalysisOptions(options);
+  const input = createPlannedInput(options.jobId, options.source);
+  return freezeCommandPlan({
+    id: `${options.jobId}:scene-change-analysis`,
+    operation: 'scene-change-analysis',
+    inputs: [input],
+    temporaryFiles: [],
+    args: [
+      '-i',
+      input.path,
+      '-an',
+      '-vf',
+      `select='gt(scene\\,${normalizedSceneThreshold(options.threshold)})',showinfo`,
+      '-frames:v',
+      String(options.maxFrames),
+      '-f',
+      'null',
+      '-',
+    ],
+    outputs: [],
+    expectedDurationSeconds: options.durationSeconds,
+    requiredCapabilities: {
+      muxers: ['null'],
+      filters: ['select', 'showinfo'],
+    },
+    diagnostics: [
+      diagnostic(
+        'bounded-scene-analysis',
+        'info',
+        `Scene analysis stops after ${options.maxFrames} qualifying frames and retains no source media.`
+      ),
+    ],
+  });
+}
+
+export function parseSceneChangeFrames(
+  logText: string
+): readonly SceneChangeFrame[] {
+  const frames: SceneChangeFrame[] = [];
+  const seenPts = new Set<number>();
+  const linePattern =
+    /^[^\n]*\bn:\s*\d+\s+pts:\s*(-?\d+)\s+pts_time:\s*([+-]?(?:\d+(?:\.\d*)?|\.\d+)(?:e[+-]?\d+)?)/gimu;
+  for (const match of logText.matchAll(linePattern)) {
+    const pts = Number(match[1]);
+    const timeSeconds = Number(match[2]);
+    if (
+      !Number.isSafeInteger(pts) ||
+      pts < 0 ||
+      !Number.isFinite(timeSeconds) ||
+      timeSeconds < 0 ||
+      seenPts.has(pts)
+    ) {
+      continue;
+    }
+    seenPts.add(pts);
+    frames.push({ pts, timeSeconds });
+    if (frames.length >= MAX_SCENE_CHANGE_FRAMES) {
+      break;
+    }
+  }
+  return Object.freeze(
+    frames
+      .sort((left, right) => left.timeSeconds - right.timeSeconds)
+      .map((frame) => Object.freeze({ ...frame }))
+  );
+}
+
+export function buildSceneThumbnailSeriesPlan(
+  options: SceneThumbnailSeriesOptions
+): FFmpegCommandPlan {
+  const frames = validateSceneFrames(
+    options.frames,
+    options.durationSeconds,
+    'Thumbnail series'
+  );
+  const input = createPlannedInput(options.jobId, options.source);
+  const extension = extensionForImageFormat(options.format);
+  const outputs = frames.map((frame, index) =>
+    createPlannedOutput(options.jobId, {
+      id: `thumbnail-${index + 1}`,
+      baseName: options.source.fileName,
+      operation: 'thumbnail',
+      suffix: `${String(index + 1).padStart(3, '0')}-${Math.round(frame.timeSeconds * 1000)}ms`,
+      extension,
+      role: 'thumbnail',
+    })
+  );
+  const size = scaleFilter(options.size);
+  const selected = frames.map((frame) => `eq(pts\\,${frame.pts})`).join('+');
+  const splitOutputs = frames
+    .map((_, index) => `[scene-source-${index}]`)
+    .join('');
+  const filtergraph = [
+    `[0:v]select='${selected}',split=${frames.length}${splitOutputs}`,
+    ...frames.map((_, index) => {
+      const filters = [
+        `select='eq(n\\,${index})'`,
+        'setpts=N/FRAME_RATE/TB',
+        ...(size ? [size] : []),
+      ];
+      return `[scene-source-${index}]${filters.join(',')}[thumb-${index}]`;
+    }),
+  ].join(';');
+  const outputArguments = outputs.flatMap((output, index) => [
+    '-map',
+    `[thumb-${index}]`,
+    '-frames:v',
+    '1',
+    ...imageQualityArguments(options.format, options.quality),
+    output.path,
+  ]);
+  return freezeCommandPlan({
+    id: `${options.jobId}:scene-thumbnail-series`,
+    operation: 'thumbnail-series',
+    inputs: [input],
+    temporaryFiles: [],
+    args: [
+      '-i',
+      input.path,
+      '-filter_complex',
+      filtergraph,
+      ...outputArguments,
+    ],
+    outputs,
+    expectedDurationSeconds: options.durationSeconds,
+    requiredCapabilities: {
+      ...imageRequirements(options.format),
+      filters: ['select', 'split', 'setpts', ...(size ? ['scale'] : [])],
+    },
+    diagnostics: [
+      diagnostic(
+        'scene-change-selection',
+        'info',
+        `${frames.length} frames are selected by exact presentation timestamp from a preceding bounded scene analysis.`
+      ),
+    ],
+  });
+}
+
 export function resolveThumbnailTimes(
  options: Pick<
    ThumbnailSeriesOptions,
@@ -271,7 +442,22 @@ export function buildContactSheetPlan(
  if (!/^(?:[a-z]{3,20}|#[0-9a-f]{6})$/iu.test(background)) {
    throw new TypeError('Background must be a named colour or #RRGGBB');
  }
+  const sceneFrames = options.sceneFrames
+    ? validateSceneFrames(
+        options.sceneFrames,
+        options.durationSeconds,
+        'Contact sheet'
+      )
+    : undefined;
+  if (sceneFrames && sceneFrames.length !== options.frameCount) {
+    throw new RangeError(
+      'Contact sheet frame count must match the analyzed scene selection'
+    );
+  }
  const input = createPlannedInput(options.jobId, options.source);
+  const fontInput = options.font
+    ? createPlannedInput(options.jobId, options.font, 'font')
+    : undefined;
  const output = createPlannedOutput(options.jobId, {
    baseName: options.source.fileName,
    operation: 'contact-sheet',
@@ -280,14 +466,20 @@ export function buildContactSheetPlan(
  });
  const fps = options.frameCount / options.durationSeconds;
  const filters = [
-    `fps=${fps.toFixed(8).replace(/0+$/u, '').replace(/\.$/u, '')}`,
+    ...(sceneFrames
+      ? [
+          `select='${sceneFrames
+            .map((frame) => `eq(pts\\,${frame.pts})`)
+            .join('+')}'`,
+        ]
+      : [`fps=${fps.toFixed(8).replace(/0+$/u, '').replace(/\.$/u, '')}`]),
    options.maintainAspect === false
      ? `scale=${options.cellWidth}:${options.cellWidth}`
      : `scale=${options.cellWidth}:-2:force_original_aspect_ratio=decrease`,
  ];
  let labelsEnabled = Boolean(options.timestampLabels || options.sourceLabel);
  const diagnostics = [];
-  if (labelsEnabled && !options.drawtextAvailable) {
+  if (labelsEnabled && (!options.drawtextAvailable || !fontInput)) {
    labelsEnabled = false;
    diagnostics.push(
      diagnostic(
@@ -302,16 +494,19 @@ export function buildContactSheetPlan(
      ? `${safePathComponent(options.source.fileName)} %{pts\\:hms}`
      : '%{pts\\:hms}';
    filters.push(
-      `drawtext=text='${text}':x=8:y=h-th-8:fontcolor=white:box=1:boxcolor=black@0.6`
+      `drawtext=fontfile='${fontInput?.path ?? ''}':text='${text}':x=8:y=h-th-8:fontcolor=white:box=1:boxcolor=black@0.6`
    );
  }
+  if (sceneFrames) {
+    filters.push('setpts=N/FRAME_RATE/TB');
+  }
  filters.push(
-    `tile=${options.columns}x${options.rows}:padding=${spacing}:margin=${spacing}:color=${background}`
+    `tile=${options.columns}x${options.rows}:nb_frames=${options.frameCount}:padding=${spacing}:margin=${spacing}:color=${background}`
  );
  return freezeCommandPlan({
    id: `${options.jobId}:contact-sheet`,
    operation: 'contact-sheet',
-    inputs: [input],
+    inputs: [input, ...(fontInput ? [fontInput] : [])],
    temporaryFiles: [],
    args: [
      '-i',
@@ -327,12 +522,101 @@ export function buildContactSheetPlan(
    expectedDurationSeconds: options.durationSeconds,
    requiredCapabilities: {
      ...imageRequirements(options.format),
-      filters: ['fps', 'scale', 'tile', ...(labelsEnabled ? ['drawtext'] : [])],
+      filters: [
+        sceneFrames ? 'select' : 'fps',
+        'scale',
+        ...(sceneFrames ? ['setpts'] : []),
+        'tile',
+        ...(labelsEnabled ? ['drawtext'] : []),
+      ],
    },
-    diagnostics,
+    diagnostics: [
+      ...diagnostics,
+      ...(sceneFrames
+        ? [
+            diagnostic(
+              'scene-change-selection',
+              'info',
+              `${sceneFrames.length} analyzed scene changes populate this contact sheet.`
+            ),
+          ]
+        : []),
+    ],
  });
 }

+function validateSceneAnalysisOptions(
+  options: Pick<
+    SceneChangeAnalysisOptions,
+    'durationSeconds' | 'threshold' | 'maxFrames'
+  >
+): void {
+  if (
+    !Number.isFinite(options.durationSeconds) ||
+    options.durationSeconds <= 0
+  ) {
+    throw new RangeError('Scene analysis source duration must be positive');
+  }
+  normalizedSceneThreshold(options.threshold);
+  if (
+    !Number.isSafeInteger(options.maxFrames) ||
+    options.maxFrames < 1 ||
+    options.maxFrames > MAX_SCENE_CHANGE_FRAMES
+  ) {
+    throw new RangeError(
+      `Scene analysis frame limit must be an integer from 1 to ${MAX_SCENE_CHANGE_FRAMES}`
+    );
+  }
+}
+
+function normalizedSceneThreshold(value: number): string {
+  if (
+    !Number.isFinite(value) ||
+    value < MIN_SCENE_CHANGE_THRESHOLD ||
+    value > MAX_SCENE_CHANGE_THRESHOLD
+  ) {
+    throw new RangeError(
+      `Scene threshold must be ${MIN_SCENE_CHANGE_THRESHOLD}–${MAX_SCENE_CHANGE_THRESHOLD}`
+    );
+  }
+  return String(Number(value.toFixed(3)));
+}
+
+function validateSceneFrames(
+  frames: readonly SceneChangeFrame[],
+  durationSeconds: number,
+  label: string
+): readonly SceneChangeFrame[] {
+  if (!Number.isFinite(durationSeconds) || durationSeconds <= 0) {
+    throw new RangeError(`${label} source duration must be positive`);
+  }
+  if (
+    frames.length < 1 ||
+    frames.length > MAX_SCENE_CHANGE_FRAMES ||
+    frames.some(
+      (frame) =>
+        !Number.isSafeInteger(frame.pts) ||
+        frame.pts < 0 ||
+        !Number.isFinite(frame.timeSeconds) ||
+        frame.timeSeconds < 0 ||
+        frame.timeSeconds >= durationSeconds
+    )
+  ) {
+    throw new RangeError(
+      `${label} scene frames must be bounded, finite points inside the source`
+    );
+  }
+  const uniquePts = new Set(frames.map((frame) => frame.pts));
+  if (uniquePts.size !== frames.length) {
+    throw new RangeError(`${label} scene frames must have unique timestamps`);
+  }
+  return Object.freeze(
+    [...frames]
+      .sort((left, right) => left.timeSeconds - right.timeSeconds)
+      .map((frame) => Object.freeze({ ...frame }))
+  );
+}
+
 function imageFilterArguments(size?: ThumbnailSize): readonly string[] {
  const filter = scaleFilter(size);
  return filter ? ['-vf', filter] : [];
--- a/src/components/AdvancedOperations.tsx
+++ b/src/components/AdvancedOperations.tsx
@@ -32,6 +32,11 @@ import {
  GENERATED_OUTPUT_LIMIT_EXPLANATION,
  MAX_GENERATED_OUTPUT_FILES,
 } from '../limits';
+import {
+  MAX_SCENE_CHANGE_FRAMES,
+  MAX_SCENE_CHANGE_THRESHOLD,
+  MIN_SCENE_CHANGE_THRESHOLD,
+} from '../commands/thumbnails';
 import {
  parseUserPresetJson,
  serializeUserPreset,
@@ -58,6 +63,7 @@ export type AdvancedCapabilityKey =
  | 'thumbnail-series'
  | 'contact-sheet'
  | 'contact-sheet-labels'
+  | 'scene-change-analysis'
  | 'metadata-write'
  | 'chapter-write'
  | 'subtitle-extract'
@@ -181,6 +187,11 @@ export type AdvancedAudioRequest =
 export type ThumbnailDistribution =
  | { readonly type: 'evenly-spaced'; readonly count: number }
  | { readonly type: 'fixed-interval'; readonly intervalSeconds: number }
+  | {
+      readonly type: 'scene-changes';
+      readonly count: number;
+      readonly threshold: number;
+    }
  | {
      readonly type: 'chapter-starts' | 'split-markers';
      readonly timesSeconds: readonly number[];
@@ -206,6 +217,9 @@ export interface ContactSheetRequest {
  readonly sourceLabel: boolean;
  readonly format: ImageFormat;
  readonly quality: number;
+  readonly selection:
+    | { readonly type: 'evenly-spaced' }
+    | { readonly type: 'scene-changes'; readonly threshold: number };
 }

 export type MetadataExecutionRequest =
@@ -556,6 +570,7 @@ export function AdvancedOperations({
          chapters={chapters}
          formatAvailability={imageFormatAvailability}
          labelAvailability={availability['contact-sheet-labels']}
+          sceneAvailability={availability['scene-change-analysis']}
          onThumbnailSeries={onThumbnailSeries}
          onContactSheet={onContactSheet}
          action={actionContext}
@@ -1442,6 +1457,7 @@ function ImagePanel({
  chapters,
  formatAvailability,
  labelAvailability,
+  sceneAvailability,
  onThumbnailSeries,
  onContactSheet,
  action,
@@ -1453,6 +1469,7 @@ function ImagePanel({
    Readonly<Record<ImageFormat, AdvancedCapabilityStatus>>
  >;
  readonly labelAvailability?: AdvancedCapabilityStatus;
+  readonly sceneAvailability?: AdvancedCapabilityStatus;
  readonly onThumbnailSeries?: RequestHandler<ThumbnailSeriesRequest>;
  readonly onContactSheet?: RequestHandler<ContactSheetRequest>;
  readonly action: ActionContext;
@@ -1474,6 +1491,10 @@ function ImagePanel({
  const [maintainAspect, setMaintainAspect] = useState(true);
  const [timestampLabels, setTimestampLabels] = useState(false);
  const [sourceLabel, setSourceLabel] = useState(false);
+  const [sceneThreshold, setSceneThreshold] = useState('0.35');
+  const [sheetSelection, setSheetSelection] = useState<
+    'evenly-spaced' | 'scene-changes'
+  >('evenly-spaced');

  const videoReason = !source
    ? 'Select a source first.'
@@ -1521,6 +1542,29 @@ function ImagePanel({
      type: distribution,
      intervalSeconds: Number(interval),
    };
+  } else if (distribution === 'scene-changes') {
+    distributionReason =
+      integerRangeReason(
+        seriesCount,
+        1,
+        MAX_SCENE_CHANGE_FRAMES,
+        'Frame count'
+      ) ??
+      numberRangeReason(
+        sceneThreshold,
+        MIN_SCENE_CHANGE_THRESHOLD,
+        MAX_SCENE_CHANGE_THRESHOLD,
+        'Scene threshold'
+      ) ??
+      (sceneAvailability?.available
+        ? undefined
+        : (sceneAvailability?.reason ??
+          'Scene-change analysis has not been verified.'));
+    resolvedDistribution = {
+      type: distribution,
+      count: Number(seriesCount),
+      threshold: Number(sceneThreshold),
+    };
  } else if (distribution === 'chapter-starts') {
    const times = chapters.map((chapter) => chapter.startSeconds);
    distributionReason =
@@ -1556,7 +1600,12 @@ function ImagePanel({
        'Timestamp and filename labels require verified drawtext and a safe local font.')
      : undefined;
  const gridReason =
-    integerRangeReason(sheetFrames, 1, 500, 'Frame count') ??
+    integerRangeReason(
+      sheetFrames,
+      1,
+      sheetSelection === 'scene-changes' ? MAX_SCENE_CHANGE_FRAMES : 500,
+      'Frame count'
+    ) ??
    integerRangeReason(sheetRows, 1, 500, 'Rows') ??
    integerRangeReason(sheetColumns, 1, 500, 'Columns') ??
    integerRangeReason(cellWidth, 32, 4096, 'Cell width') ??
@@ -1571,7 +1620,19 @@ function ImagePanel({
    gridReason ??
    numberRangeReason(quality, 1, 100, 'Quality') ??
    formatReason ??
-    labelReason;
+    labelReason ??
+    (sheetSelection === 'scene-changes'
+      ? (numberRangeReason(
+          sceneThreshold,
+          MIN_SCENE_CHANGE_THRESHOLD,
+          MAX_SCENE_CHANGE_THRESHOLD,
+          'Scene threshold'
+        ) ??
+        (sceneAvailability?.available
+          ? undefined
+          : (sceneAvailability?.reason ??
+            'Scene-change analysis has not been verified.')))
+      : undefined);

  return (
    <div className="advanced-operations__section-grid">
@@ -1597,6 +1658,12 @@ function ImagePanel({
          >
            <option value="evenly-spaced">Evenly spaced</option>
            <option value="fixed-interval">Fixed interval</option>
+            <option
+              value="scene-changes"
+              disabled={!sceneAvailability?.available}
+            >
+              Scene changes
+            </option>
            <option value="chapter-starts" disabled={chapters.length === 0}>
              Chapter starts
            </option>
@@ -1605,12 +1672,17 @@ function ImagePanel({
            </option>
          </select>
        </label>
-        {distribution === 'evenly-spaced' ? (
+        {distribution === 'evenly-spaced' ||
+        distribution === 'scene-changes' ? (
          <NumberField
            label="Number of frames"
            value={seriesCount}
            min={1}
-            max={MAX_GENERATED_OUTPUT_FILES}
+            max={
+              distribution === 'scene-changes'
+                ? MAX_SCENE_CHANGE_FRAMES
+                : MAX_GENERATED_OUTPUT_FILES
+            }
            onChange={setSeriesCount}
          />
        ) : null}
@@ -1625,6 +1697,16 @@ function ImagePanel({
            onChange={setInterval}
          />
        ) : null}
+        {distribution === 'scene-changes' ? (
+          <NumberField
+            label="Scene sensitivity threshold"
+            value={sceneThreshold}
+            min={MIN_SCENE_CHANGE_THRESHOLD}
+            max={MAX_SCENE_CHANGE_THRESHOLD}
+            step={0.01}
+            onChange={setSceneThreshold}
+          />
+        ) : null}
        <ImageSettings
          width={width}
          height={height}
@@ -1673,11 +1755,32 @@ function ImagePanel({
          </div>
        </header>
        <div className="advanced-form-grid advanced-form-grid--three">
+          <label className="advanced-field">
+            <span>Frame selection</span>
+            <select
+              value={sheetSelection}
+              onChange={(event) =>
+                setSheetSelection(
+                  event.currentTarget.value as 'evenly-spaced' | 'scene-changes'
+                )
+              }
+            >
+              <option value="evenly-spaced">Evenly spaced</option>
+              <option
+                value="scene-changes"
+                disabled={!sceneAvailability?.available}
+              >
+                Scene changes
+              </option>
+            </select>
+          </label>
          <NumberField
            label="Frames"
            value={sheetFrames}
            min={1}
-            max={500}
+            max={
+              sheetSelection === 'scene-changes' ? MAX_SCENE_CHANGE_FRAMES : 500
+            }
            onChange={setSheetFrames}
          />
          <NumberField
@@ -1716,6 +1819,16 @@ function ImagePanel({
            onChange={setBackground}
          />
        </div>
+        {sheetSelection === 'scene-changes' ? (
+          <NumberField
+            label="Contact-sheet scene threshold"
+            value={sceneThreshold}
+            min={MIN_SCENE_CHANGE_THRESHOLD}
+            max={MAX_SCENE_CHANGE_THRESHOLD}
+            step={0.01}
+            onChange={setSceneThreshold}
+          />
+        ) : null}
        <div className="advanced-check-grid">
          <CheckField
            label="Maintain aspect ratio"
@@ -1769,6 +1882,13 @@ function ImagePanel({
                sourceLabel,
                format,
                quality: Number(quality),
+                selection:
+                  sheetSelection === 'scene-changes'
+                    ? {
+                        type: 'scene-changes',
+                        threshold: Number(sceneThreshold),
+                      }
+                    : { type: 'evenly-spaced' },
              },
              'Contact sheet added to the local queue.'
            )
--- a/src/components/HelpDialog.tsx
+++ b/src/components/HelpDialog.tsx
@@ -1,5 +1,6 @@
 import { useEffect, useRef } from 'react';
 import applicationLicenseUrl from '../../LICENSE?url&no-inline';
+import dejavuFontLicenseUrl from '../../LICENSES/DEJAVU_FONTS.txt?url&no-inline';
 import ffmpegWasmLicenseUrl from '../../LICENSES/ffmpeg.wasm-MIT.txt?url&no-inline';
 import gplLicenseUrl from '../../LICENSES/GPL-2.0-or-later.txt?url&no-inline';
 import licenseStatusUrl from '../../LICENSES/README.md?url&no-inline';
@@ -7,7 +8,7 @@ import sourceRecordUrl from '../../SOURCE.md?url&no-inline';
 import thirdPartyNoticesUrl from '../../THIRD_PARTY_NOTICES.md?url&no-inline';
 import {
  APP_VERSION,
-  FFMPEG_CORE_VERSION,
+  FFMPEG_CORE_BUILD_ID,
  FFMPEG_ENGINE_VERSION,
  FFMPEG_UTIL_VERSION,
  FFMPEG_WRAPPER_VERSION,
@@ -101,7 +102,7 @@ export function HelpDialog({ open, onClose }: HelpDialogProps) {
            </div>
            <div>
              <dt>FFmpeg WASM cores</dt>
-              <dd>{FFMPEG_CORE_VERSION} · ST &amp; MT</dd>
+              <dd>{FFMPEG_CORE_BUILD_ID} · ST &amp; MT</dd>
            </div>
            <div>
              <dt>ffmpeg.wasm utilities</dt>
@@ -156,6 +157,16 @@ export function HelpDialog({ open, onClose }: HelpDialogProps) {
                    GPL text
                  </a>
                </li>
+                <li>
+                  DejaVu Sans 2.37 — Bitstream Vera and Arev font terms
+                  <a
+                    href={dejavuFontLicenseUrl}
+                    target="_blank"
+                    rel="noreferrer"
+                  >
+                    Font licence
+                  </a>
+                </li>
                <li>
                  FFmpeg, linked codecs, Toolbox SDK, React and other runtime
                  packages retain their respective terms.
--- a/src/components/MediaPreview.tsx
+++ b/src/components/MediaPreview.tsx
@@ -3,6 +3,9 @@ import type { ImportedMediaAsset } from '../app/application-state';
 import {
  assessBrowserPlayback,
  assessGeneratedResultPreview,
+  isAudioMimeType,
+  isVideoMimeType,
+  mimeTypeFromFileName,
  type MediaProbe,
 } from '../media';
 import { renderWaveformToCanvas, type WaveformPeakData } from '../waveform';
@@ -47,15 +50,31 @@ export function MediaPreview({
  const mediaElement = useRef<HTMLMediaElement>(null);
  const sourceUrl = result?.objectUrl ?? asset?.objectUrl;
  const playbackFailed = sourceUrl === failedSourceUrl;
+  const fileMimeType = asset?.file.type;
+  const declaredSourceMimeType =
+    fileMimeType &&
+    (isVideoMimeType(fileMimeType) || isAudioMimeType(fileMimeType))
+      ? fileMimeType
+      : asset
+        ? mimeTypeFromFileName(asset.file.name)
+        : undefined;
  const hasVideo = result
    ? result.mimeType.startsWith('video/')
-    : asset?.probe?.streams.some(
+    : asset?.probe
+      ? asset.probe.streams.some(
          (stream) =>
            stream.type === 'video' && stream.disposition.attached_pic !== true
-      ) === true;
+        )
+      : declaredSourceMimeType
+        ? isVideoMimeType(declaredSourceMimeType)
+        : false;
  const hasAudio = result
    ? result.mimeType.startsWith('audio/')
-    : asset?.probe?.streams.some((stream) => stream.type === 'audio') === true;
+    : asset?.probe
+      ? asset.probe.streams.some((stream) => stream.type === 'audio')
+      : declaredSourceMimeType
+        ? isAudioMimeType(declaredSourceMimeType)
+        : false;
  const hasImage = result?.mimeType.startsWith('image/') === true;
  const resultPlayback = useMemo(() => {
    if (!result) return undefined;
@@ -186,7 +205,10 @@ export function MediaPreview({
            ? resultPlayback?.previewable === false
              ? `Download only · ${result.name}`
              : `Generated result · ${result.name}`
-            : (playback?.reason ?? 'Local source preview')}
+            : (playback?.reason ??
+              (asset?.phase === 'probing'
+                ? 'Local source preview · Media inspection continues in the background.'
+                : 'Local source preview'))}
        </span>
        {needsProxy && !proxySettings ? (
          <button type="button" className="text-button" onClick={onCreateProxy}>
--- a/src/components/QuickConvert.tsx
+++ b/src/components/QuickConvert.tsx
@@ -16,6 +16,7 @@ import {
  presetAvailability,
 } from '../presets/preset-registry';
 import { formatBytes, formatDuration } from '../app/application-state';
+import { FFMPEG_OPUS_REGRESSION_VERIFIED } from '../version';
 import { Icon } from './Icon';

 export type QuickOperation = 'convert' | 'remux';
@@ -139,7 +140,8 @@ export function QuickConvert({
          engineState.capabilities
        )
      : undefined;
-  const opusNeedsRegressionTest = preset?.audio?.codec === 'libopus';
+  const opusBlockedByPinnedCore =
+    preset?.audio?.codec === 'libopus' && !FFMPEG_OPUS_REGRESSION_VERIFIED;
  const presetNeedsMissingAudio =
    preset?.kind === 'audio' && effectiveSelection.audio.length === 0;
  const remuxStreams: readonly RemuxStream[] = streams.flatMap((stream) =>
@@ -186,7 +188,7 @@ export function QuickConvert({
      ? !remuxMuxerMissing && remuxErrors.length === 0
      : preset !== undefined &&
        availability?.status !== 'unavailable' &&
-        !opusNeedsRegressionTest &&
+        !opusBlockedByPinnedCore &&
        !presetNeedsMissingAudio);

  const presetOption = (entry: ExportPreset) => {
@@ -199,8 +201,8 @@ export function QuickConvert({
        ? presetAvailability({ requirements }, engineState.capabilities)
        : undefined;
    const reason =
-      entry.audio?.codec === 'libopus'
-        ? 'Opus awaits a pinned-core regression test'
+      entry.audio?.codec === 'libopus' && !FFMPEG_OPUS_REGRESSION_VERIFIED
+        ? 'the reviewed core has not passed the ST/MT Opus regression encode'
        : entryAvailability?.status === 'unavailable'
          ? entryAvailability.reasons.join(', ')
          : undefined;
@@ -455,11 +457,11 @@ export function QuickConvert({
          Select at least one output stream.
        </p>
      ) : null}
-      {opusNeedsRegressionTest ? (
+      {opusBlockedByPinnedCore ? (
        <p className="notice notice--warning">
          <Icon name="warning" />
-          Opus export is held back until the pinned core passes its browser
-          regression test.
+          Opus export is disabled until the reviewed core passes its non-empty
+          encode and re-probe gate in both engine modes.
        </p>
      ) : null}

--- a/src/components/StructuralOperations.css
+++ b/src/components/StructuralOperations.css
@@ -244,7 +244,8 @@
  font-weight: 740;
 }

-.structural-field select {
+.structural-field select,
+.structural-field input {
  width: 100%;
  min-height: 2.5rem;
  padding: 0.48rem 0.62rem;
@@ -402,6 +403,7 @@
 }

 .structural-field select:focus-visible,
+.structural-field input:focus-visible,
 .structural-operations input:focus-visible,
 .structural-operations button:focus-visible {
  outline: 3px solid var(--toolbox-focus);
--- a/src/components/StructuralOperations.tsx
+++ b/src/components/StructuralOperations.tsx
@@ -2,7 +2,11 @@ import { useId, useState } from 'react';
 import './StructuralOperations.css';

 export type StructuralCapabilityKey =
-  'trim-fast' | 'trim-accurate' | 'concat-fast' | 'concat-normalized';
+  | 'trim-fast'
+  | 'trim-accurate'
+  | 'concat-fast'
+  | 'concat-normalized'
+  | 'concat-crossfade';

 export interface StructuralCapabilityStatus {
  readonly available: boolean;
@@ -35,6 +39,7 @@ export interface StructuralTimelineClip {
  readonly hasAudio: boolean;
  readonly hasVideo: boolean;
  readonly hasSubtitles: boolean;
+  readonly durationSeconds?: number;
 }

 export interface StructuralCompatibilityDiagnostic {
@@ -92,6 +97,7 @@ export type StructuralConcatRequest =
      readonly presetId: string;
      readonly missingAudioPolicy: MissingAudioPolicy;
      readonly subtitlePolicy: NormalizedSubtitlePolicy;
+      readonly crossfadeSeconds: number;
    };

 type RequestHandler<T> = (request: T) => void | Promise<void>;
@@ -135,6 +141,7 @@ export function StructuralOperations({
  const [subtitlePolicy, setSubtitlePolicy] = useState<
    NormalizedSubtitlePolicy | ''
  >('');
+  const [crossfadeSeconds, setCrossfadeSeconds] = useState('0');
  const [pending, setPending] = useState(false);
  const [status, setStatus] = useState<string>();

@@ -156,6 +163,7 @@ export function StructuralOperations({
    preset: concatPreset,
    missingAudioPolicy,
    subtitlePolicy,
+    crossfadeSeconds,
    availability,
    connected: Boolean(onConcat),
    busy: busy || pending,
@@ -445,6 +453,30 @@ export function StructuralOperations({
                )}
                onChange={setSubtitlePolicy}
              />
+              <label
+                className="structural-field"
+                htmlFor={`${componentId}-crossfade`}
+              >
+                <span>Crossfade duration</span>
+                <input
+                  id={`${componentId}-crossfade`}
+                  type="number"
+                  aria-label="Crossfade duration"
+                  min="0"
+                  max="10"
+                  step="0.04"
+                  inputMode="decimal"
+                  value={crossfadeSeconds}
+                  disabled={busy || pending}
+                  onChange={(event) =>
+                    setCrossfadeSeconds(event.currentTarget.value)
+                  }
+                />
+                <small>
+                  0 keeps hard cuts. A value from 0.04–10 seconds overlaps video
+                  and, when retained, audio at every edit.
+                </small>
+              </label>
            </>
          )}

@@ -488,6 +520,7 @@ export function StructuralOperations({
                  presetId: concatPreset.id,
                  missingAudioPolicy,
                  subtitlePolicy,
+                  crossfadeSeconds: Number(crossfadeSeconds),
                },
                'Normalized concat queued.'
              );
@@ -856,6 +889,7 @@ function reasonForConcat({
  preset,
  missingAudioPolicy,
  subtitlePolicy,
+  crossfadeSeconds,
  availability,
  connected,
  busy,
@@ -865,6 +899,7 @@ function reasonForConcat({
  readonly preset: StructuralExportPresetOption | undefined;
  readonly missingAudioPolicy: MissingAudioPolicy | '';
  readonly subtitlePolicy: NormalizedSubtitlePolicy | '';
+  readonly crossfadeSeconds: string;
  readonly availability: StructuralOperationsProps['availability'];
  readonly connected: boolean;
  readonly busy: boolean;
@@ -924,13 +959,39 @@ function reasonForConcat({
    ) {
      return 'This sequence contains subtitles. Explicitly drop all subtitles, or remove them before normalized concat.';
    }
+    const crossfade = Number(crossfadeSeconds);
+    if (
+      !Number.isFinite(crossfade) ||
+      crossfade < 0 ||
+      (crossfade > 0 && (crossfade < 0.04 || crossfade > 10))
+    ) {
+      return 'Crossfade duration must be 0, or a value from 0.04–10 seconds.';
+    }
+    if (crossfade > 0) {
+      for (const [index, clip] of timeline.clips.entries()) {
+        if (clip.durationSeconds === undefined) {
+          continue;
+        }
+        const required =
+          index === 0 || index === timeline.clips.length - 1
+            ? crossfade
+            : crossfade * 2;
+        if (clip.durationSeconds < required) {
+          return `Clip ${index + 1} is too short for ${crossfade} second crossfades at its edit boundaries.`;
+        }
+      }
+    }
  }
  if (!connected) {
    return 'This action has not been connected to the job runner.';
  }
-  return capabilityReason(
+  const baseReason = capabilityReason(
    availability?.[mode === 'fast' ? 'concat-fast' : 'concat-normalized']
  );
+  if (baseReason || mode === 'fast' || Number(crossfadeSeconds) === 0) {
+    return baseReason;
+  }
+  return capabilityReason(availability?.['concat-crossfade']);
 }

 function capabilityReason(
--- a/src/ffmpeg/EngineManager.ts
+++ b/src/ffmpeg/EngineManager.ts
@@ -32,6 +32,9 @@ import {
 type FFmpegFactory = () => Promise<FFmpegAdapter>;

 export const DEFAULT_JOB_TIMEOUT_MILLISECONDS = 4 * 60 * 60 * 1_000;
+export const MIN_PROBE_TIMEOUT_MILLISECONDS = 30_000;
+export const MAX_PROBE_TIMEOUT_MILLISECONDS = 5 * 60_000;
+export const PROBE_BUDGET_BYTES_PER_SECOND = 2 * 1024 * 1024;
 export const MULTITHREAD_CODEC_THREAD_LIMIT = 2;
 /**
 * The pinned Emscripten core can retain native heap state across heterogeneous
@@ -55,6 +58,19 @@ export function shouldRecycleExecutionCore(
  );
 }

+export function probeTimeoutMilliseconds(inputBytes: number): number {
+  if (!Number.isFinite(inputBytes) || inputBytes <= 0) {
+    return MIN_PROBE_TIMEOUT_MILLISECONDS;
+  }
+  const sizeAwareBudget = Math.ceil(
+    (inputBytes / PROBE_BUDGET_BYTES_PER_SECOND) * 1_000
+  );
+  return Math.min(
+    MAX_PROBE_TIMEOUT_MILLISECONDS,
+    Math.max(MIN_PROBE_TIMEOUT_MILLISECONDS, sizeAwareBudget)
+  );
+}
+
 async function defaultFFmpegFactory(): Promise<FFmpegAdapter> {
  const { FFmpeg } = await import('@ffmpeg/ffmpeg');
  return new FFmpeg();
@@ -521,8 +537,18 @@ export class EngineManager {
    };
  }

-  async probe(file: File, timeoutMilliseconds = 30_000): Promise<ProbeResult> {
+  async probe(
+    file: File,
+    timeoutMilliseconds = probeTimeoutMilliseconds(file.size),
+    signal?: AbortSignal
+  ): Promise<ProbeResult> {
+    if (signal?.aborted) {
+      throw new EngineError('cancelled', 'The media probe was cancelled.');
+    }
    await this.initialize();
+    if (signal?.aborted) {
+      throw new EngineError('cancelled', 'The media probe was cancelled.');
+    }
    const engine = this.#engine;
    const mode = this.#mode;
    if (!engine || !mode || this.#state.status !== 'ready') {
@@ -537,6 +563,10 @@ export class EngineManager {

    const id = crypto.randomUUID();
    const mounted = await mountJobFiles(engine, id, [file], ['probe.json']);
+    if (signal?.aborted) {
+      await mounted.cleanup();
+      throw new EngineError('cancelled', 'The media probe was cancelled.');
+    }
    const probeOutput = mounted.outputPaths[0];
    const inputPath = mounted.inputPaths[0];
    if (!probeOutput || !inputPath) {
@@ -565,7 +595,15 @@ export class EngineManager {
      type: mounted.inputMode === 'workerfs' ? 'stdout' : 'stderr',
      message: describeMountedInputAccess(mounted),
    });
-    const watchdog = setTimeout(() => this.cancelActive(), timeoutMilliseconds);
+    let timedOut = false;
+    const watchdog = setTimeout(() => {
+      timedOut = true;
+      void this.cancelActive();
+    }, timeoutMilliseconds);
+    const cancelOnAbort = () => {
+      void this.cancelActive();
+    };
+    signal?.addEventListener('abort', cancelOnAbort, { once: true });
    try {
      const exitCode = await engine.ffprobe([
        '-v',
@@ -630,6 +668,13 @@ export class EngineManager {
      };
    } catch (error) {
      if (this.#cancelledJobIds.delete(activeProbeId)) {
+        if (timedOut) {
+          throw new EngineError(
+            'probe-failed',
+            `Media inspection exceeded its ${String(Math.ceil(timeoutMilliseconds / 1_000))}-second safety limit.`,
+            { cause: error }
+          );
+        }
        throw new EngineError('cancelled', 'The media probe was cancelled.', {
          cause: error,
        });
@@ -641,6 +686,7 @@ export class EngineManager {
            details: this.#logs.text(),
          });
    } finally {
+      signal?.removeEventListener('abort', cancelOnAbort);
      clearTimeout(watchdog);
      this.#activeJobId = null;
      this.#machineProgressLines = [];
--- a/src/ffmpeg/asset-urls.ts
+++ b/src/ffmpeg/asset-urls.ts
@@ -1,5 +1,5 @@
 import type { EngineMode } from './ffmpeg.types';
-import { FFMPEG_CORE_VERSION } from '../version';
+import { FFMPEG_CORE_BUILD_ID } from '../version';

 export function resolveFromAppBase(
  relativePath: string,
@@ -22,8 +22,8 @@ export function getCoreAssetUrls(
 ): CoreAssetUrls {
  const directory =
    mode === 'multithread'
-      ? `vendor/ffmpeg/${FFMPEG_CORE_VERSION}/mt/`
-      : `vendor/ffmpeg/${FFMPEG_CORE_VERSION}/st/`;
+      ? `vendor/ffmpeg/${FFMPEG_CORE_BUILD_ID}/mt/`
+      : `vendor/ffmpeg/${FFMPEG_CORE_BUILD_ID}/st/`;
  const base = resolver(directory);
  const urls: CoreAssetUrls = {
    coreURL: new URL('ffmpeg-core.js', base).href,
--- a/src/toolbox/manifest.source.json
+++ b/src/toolbox/manifest.source.json
@@ -3,7 +3,7 @@
  "schemaVersion": 1,
  "id": "de.add-ideas.av-tools",
  "name": "Audio & Video Tools",
-  "version": "0.1.0",
+  "version": "0.2.0",
  "description": "Convert and lightly edit audio and video locally in the browser.",
  "entry": "./",
  "icon": "./favicon.svg",
@@ -48,10 +48,10 @@
    }
  ],
  "assets": [
-    "./vendor/ffmpeg/0.12.10/st/ffmpeg-core.js",
-    "./vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm",
-    "./vendor/ffmpeg/0.12.10/mt/ffmpeg-core.js",
-    "./vendor/ffmpeg/0.12.10/mt/ffmpeg-core.wasm",
-    "./vendor/ffmpeg/0.12.10/mt/ffmpeg-core.worker.js"
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.js",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.js",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.wasm",
+    "./vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.worker.js"
  ]
 }
--- a/src/version.ts
+++ b/src/version.ts
@@ -1,5 +1,7 @@
-export const APP_VERSION = '0.1.0';
+export const APP_VERSION = '0.2.0';
 export const FFMPEG_WRAPPER_VERSION = '0.12.15';
 export const FFMPEG_UTIL_VERSION = '0.12.2';
 export const FFMPEG_CORE_VERSION = '0.12.10';
+export const FFMPEG_CORE_BUILD_ID = '0.12.10-reviewed-stack5m.1';
 export const FFMPEG_ENGINE_VERSION = 'n5.1.4';
+export const FFMPEG_OPUS_REGRESSION_VERIFIED = true;
--- a/tests/browser/application.spec.ts
+++ b/tests/browser/application.spec.ts
@@ -191,12 +191,12 @@ test.describe('nested static deployment and Toolbox context', () => {

    const coreScript = runtime.responses.find((response) =>
      response.url.endsWith(
-        '/deep/nested/av/vendor/ffmpeg/0.12.10/st/ffmpeg-core.js'
+        '/deep/nested/av/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.js'
      )
    );
    const coreWasm = runtime.responses.find((response) =>
      response.url.endsWith(
-        '/deep/nested/av/vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm'
+        '/deep/nested/av/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm'
      )
    );
    expect(coreScript).toMatchObject({
--- a/tests/browser/ffmpeg-runtime.spec.ts
+++ b/tests/browser/ffmpeg-runtime.spec.ts
@@ -75,9 +75,9 @@ test.describe.serial('real pinned FFmpeg browser runtime', () => {
    );

    const expectedAssets = [
-      '/vendor/ffmpeg/0.12.10/mt/ffmpeg-core.js',
-      '/vendor/ffmpeg/0.12.10/mt/ffmpeg-core.wasm',
-      '/vendor/ffmpeg/0.12.10/mt/ffmpeg-core.worker.js',
+      '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.js',
+      '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.wasm',
+      '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.worker.js',
    ];
    for (const suffix of expectedAssets) {
      expect(
@@ -87,11 +87,15 @@ test.describe.serial('real pinned FFmpeg browser runtime', () => {
      ).toBe(true);
    }
    const wasm = runtime.responses.find((response) =>
-      response.url.endsWith('/vendor/ffmpeg/0.12.10/mt/ffmpeg-core.wasm')
+      response.url.endsWith(
+        '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.wasm'
+      )
    );
    expect(wasm?.contentType).toContain('application/wasm');
    expect(
-      runtime.requests.some((url) => url.includes('/vendor/ffmpeg/0.12.10/st/'))
+      runtime.requests.some((url) =>
+        url.includes('/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/')
+      )
    ).toBe(false);

    await mediaInput(page).setInputFiles(PRIMARY_FIXTURE);
@@ -119,8 +123,9 @@ test.describe.serial('real pinned FFmpeg browser runtime', () => {
    page,
  }) => {
    const runtime = observeRuntime(page);
-    await page.route('**/vendor/ffmpeg/0.12.10/mt/**', (route) =>
-      route.abort('failed')
+    await page.route(
+      '**/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/**',
+      (route) => route.abort('failed')
    );
    await page.goto('/');
    const environment = await page.evaluate(() => ({
@@ -147,13 +152,17 @@ test.describe.serial('real pinned FFmpeg browser runtime', () => {
      )
    ).toBeVisible();
    expect(
-      runtime.requests.some((url) => url.includes('/vendor/ffmpeg/0.12.10/mt/'))
+      runtime.requests.some((url) =>
+        url.includes('/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/mt/')
+      )
    ).toBe(true);
    expect(
      runtime.responses.some(
        (response) =>
          response.status === 200 &&
-          response.url.endsWith('/vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm')
+          response.url.endsWith(
+            '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm'
+          )
      )
    ).toBe(true);
    expect(runtime.pageErrors).toEqual([]);
@@ -247,7 +256,9 @@ test.describe.serial('real pinned FFmpeg browser runtime', () => {

    expect(
      runtime.requests.some((url) =>
-        url.endsWith('/vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm')
+        url.endsWith(
+          '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm'
+        )
      )
    ).toBe(true);
    assertLocalOnly(runtime);
@@ -303,7 +314,9 @@ test.describe.serial('real pinned FFmpeg browser runtime', () => {
    ).toHaveCount(4);
    expect(
      runtime.requests.filter((url) =>
-        url.endsWith('/vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm')
+        url.endsWith(
+          '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm'
+        )
      )
    ).toHaveLength(2);
    assertLocalOnly(runtime);
@@ -356,4 +369,43 @@ test.describe.serial('real pinned FFmpeg browser runtime', () => {
    await expect(page.getByRole('alert')).toHaveCount(0);
    assertLocalOnly(runtime);
  });
+
+  test('removes active and queued inspections without applying stale probe results', async ({
+    page,
+  }) => {
+    const runtime = observeRuntime(page);
+    await page.goto('/');
+    await selectSingleThread(page);
+
+    await mediaInput(page).setInputFiles([
+      cancellationFixture.filePath,
+      PRIMARY_FIXTURE,
+    ]);
+    const activeName = basename(cancellationFixture.filePath);
+    const activeCard = page.locator('.media-card').filter({
+      hasText: activeName,
+    });
+    const queuedCard = page.locator('.media-card').filter({
+      hasText: 'pattern-av.mp4',
+    });
+    await expect(activeCard.locator('.phase--probing')).toBeVisible({
+      timeout: 30_000,
+    });
+    await expect(queuedCard.locator('.phase--queued')).toBeVisible();
+
+    await page.getByRole('button', { name: 'Remove pattern-av.mp4' }).click();
+    await page.getByRole('button', { name: `Remove ${activeName}` }).click();
+    await expect(page.locator('.media-card')).toHaveCount(0);
+    await expect(
+      page.getByRole('button', { name: 'Choose files' })
+    ).toBeEnabled({ timeout: 120_000 });
+
+    await mediaInput(page).setInputFiles(PRIMARY_FIXTURE);
+    await expect(page.locator('.source-summary .phase--ready')).toHaveText(
+      'Ready',
+      { timeout: 120_000 }
+    );
+    await expect(page.getByRole('alert')).toHaveCount(0);
+    assertLocalOnly(runtime);
+  });
 });
--- a/tests/browser/large-media-preview.spec.ts
+++ b/tests/browser/large-media-preview.spec.ts
@@ -0,0 +1,61 @@
+/// <reference types="node" />
+
+import { existsSync } from 'node:fs';
+import { basename } from 'node:path';
+import { expect, test } from '@playwright/test';
+
+const mediaPath = process.env.AV_TOOLS_LARGE_MEDIA;
+
+test('plays a recognized large local video while inspection continues', async ({
+  page,
+}) => {
+  test.skip(
+    !mediaPath || !existsSync(mediaPath),
+    'Set AV_TOOLS_LARGE_MEDIA to a local video for this opt-in evidence run.'
+  );
+  test.setTimeout(360_000);
+  await page.goto('/');
+
+  const startedAt = Date.now();
+  await page
+    .locator('input[type="file"][accept*="audio"]')
+    .first()
+    .setInputFiles(mediaPath as string);
+  const name = basename(mediaPath as string);
+  const card = page.locator('.media-card').filter({ hasText: name });
+  const preview = page.locator('.preview video');
+  await expect(preview).toBeVisible({ timeout: 15_000 });
+  const previewVisibleMilliseconds = Date.now() - startedAt;
+  expect(previewVisibleMilliseconds).toBeLessThan(15_000);
+  await expect(card.locator('.phase--probing')).toBeVisible();
+
+  const elementIdentity = await preview.evaluate((element) => {
+    element.dataset.evidenceIdentity = crypto.randomUUID();
+    return element.dataset.evidenceIdentity;
+  });
+  await preview.evaluate(async (element) => {
+    const video = element as HTMLVideoElement;
+    video.muted = true;
+    await video.play();
+  });
+  await expect
+    .poll(
+      () =>
+        preview.evaluate(
+          (element) => (element as HTMLVideoElement).currentTime
+        ),
+      {
+        timeout: 15_000,
+      }
+    )
+    .toBeGreaterThan(0);
+
+  await expect(card.locator('.phase--ready')).toBeVisible({
+    timeout: 330_000,
+  });
+  await expect(preview).toHaveAttribute(
+    'data-evidence-identity',
+    elementIdentity
+  );
+  await expect(page.getByRole('alert')).toHaveCount(0);
+});
--- a/tests/browser/operation-matrix.spec.ts
+++ b/tests/browser/operation-matrix.spec.ts
@@ -149,7 +149,7 @@ function probe(filePath: string): {
    tags?: Record<string, string>;
    disposition?: Record<string, number>;
  }>;
-  format?: { tags?: Record<string, string> };
+  format?: { duration?: string; tags?: Record<string, string> };
  chapters?: Array<{ tags?: Record<string, string> }>;
 } {
  return JSON.parse(
@@ -547,6 +547,31 @@ test.describe.serial('real ffmpeg.wasm operation matrix', () => {
          expect.objectContaining({ codec_name: 'aac', codec_type: 'audio' }),
        ])
      );
+
+      await structural.getByLabel('Crossfade duration').fill('0.2');
+      const crossfadeAction = structural.getByRole('button', {
+        name: 'Export normalized concat',
+      });
+      if (await crossfadeAction.isEnabled()) {
+        const [crossfadeCard] = await runForResults(
+          page,
+          () => crossfadeAction.click(),
+          ['compatible-a-concat.mp4'],
+          { verifyMedia: true }
+        );
+        const crossfadeDuration = Number(
+          probe((await downloadResult(page, crossfadeCard as Locator)).filePath)
+            .format?.duration
+        );
+        expect(crossfadeDuration).toBeGreaterThan(1.35);
+        expect(crossfadeDuration).toBeLessThan(1.75);
+      } else {
+        await expect(
+          structural.getByText(
+            /required browser and FFmpeg capabilities have not been verified|filter (?:x|a)fade/iu
+          )
+        ).toBeVisible();
+      }
    });

    const advanced = page.locator('.advanced-operations');
@@ -687,6 +712,72 @@ test.describe.serial('real ffmpeg.wasm operation matrix', () => {
        statSync((await downloadResult(page, sheetCard as Locator)).filePath)
          .size
      ).toBeGreaterThan(500);
+
+      await importMedia(page, ['pattern-av.mp4']);
+      const patternClip = page
+        .locator('.timeline-clip')
+        .filter({ hasText: 'pattern-av.mp4' });
+      await patternClip.locator('.timeline-clip__main').click();
+      const imageSelection = advanced.getByLabel('Frame selection').first();
+      const sceneOption = imageSelection.locator(
+        'option[value="scene-changes"]'
+      );
+      if (!(await sceneOption.isDisabled())) {
+        await imageSelection.selectOption('scene-changes');
+        await advanced.getByLabel('Number of frames').fill('2');
+        await advanced.getByLabel('Scene sensitivity threshold').fill('0.01');
+        await runForResults(
+          page,
+          () =>
+            advanced
+              .getByRole('button', { name: 'Generate thumbnail series' })
+              .click(),
+          [
+            'pattern-av-thumbnail-001-83ms.jpg',
+            'pattern-av-thumbnail-002-1000ms.jpg',
+          ]
+        );
+
+        const contactSelection = advanced.getByLabel('Frame selection').nth(1);
+        await contactSelection.selectOption('scene-changes');
+        await advanced.getByLabel('Contact-sheet scene threshold').fill('0.01');
+        await advanced
+          .getByRole('spinbutton', { name: 'Frames', exact: true })
+          .fill('2');
+        await advanced
+          .getByRole('spinbutton', { name: 'Rows', exact: true })
+          .fill('1');
+        await advanced
+          .getByRole('spinbutton', { name: 'Columns', exact: true })
+          .fill('2');
+        const timestampLabels = advanced.getByLabel('Timestamp labels');
+        if (await timestampLabels.isEnabled()) {
+          await timestampLabels.check();
+          await advanced.getByLabel('Source filename label').check();
+        }
+        const [sceneSheetCard] = await runForResults(
+          page,
+          () =>
+            advanced
+              .getByRole('button', { name: 'Generate contact sheet' })
+              .click(),
+          ['pattern-av-contact-sheet.jpg']
+        );
+        expect(
+          statSync(
+            (await downloadResult(page, sceneSheetCard as Locator)).filePath
+          ).size
+        ).toBeGreaterThan(500);
+      }
+
+      await patternClip.getByRole('button', { name: 'Remove clip' }).click();
+      await expect(patternClip).toHaveCount(0);
+      await page
+        .locator('.timeline-clip')
+        .filter({ hasText: 'compatible-a.mp4' })
+        .first()
+        .locator('.timeline-clip__main')
+        .click();
    });

    await test.step('single frame and a transformed timeline with audio/video fades', async () => {
@@ -988,7 +1079,9 @@ test.describe.serial('real ffmpeg.wasm operation matrix', () => {

    expect(
      runtime.requests.some((url) =>
-        url.endsWith('/vendor/ffmpeg/0.12.10/st/ffmpeg-core.wasm')
+        url.endsWith(
+          '/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/st/ffmpeg-core.wasm'
+        )
      )
    ).toBe(true);
    assertLocalOnly(runtime);
--- a/tests/integration/command-runtime-native.test.ts
+++ b/tests/integration/command-runtime-native.test.ts
@@ -28,6 +28,8 @@ import {
  buildPeakNormalizationPlan,
  buildPreviewProxyPlan,
  buildRemuxPlan,
+  buildSceneChangeAnalysisPlan,
+  buildSceneThumbnailSeriesPlan,
  buildSingleThumbnailPlan,
  buildSplitPlan,
  buildStaticWaveformPlan,
@@ -44,6 +46,7 @@ import {
  createConcatListEntries,
  parseLoudnessMeasurement,
  parsePeakMeasurement,
+  parseSceneChangeFrames,
  resolveThumbnailTimes,
  streamMapArguments,
  type ConcatSource,
@@ -63,8 +66,16 @@ const NATIVE_SUBTITLES_FILTER_AVAILABLE =
      encoding: 'utf8',
    }).stdout ?? ''
  );
+const NATIVE_DRAWTEXT_FILTER_AVAILABLE =
+  NATIVE_FFMPEG_AVAILABLE &&
+  /\bdrawtext\b/u.test(
+    spawnSync('ffmpeg', ['-hide_banner', '-filters'], {
+      encoding: 'utf8',
+    }).stdout ?? ''
+  );
 const describeNative = NATIVE_FFMPEG_AVAILABLE ? describe : describe.skip;
 const itNativeSubtitles = NATIVE_SUBTITLES_FILTER_AVAILABLE ? it : it.skip;
+const itNativeDrawtext = NATIVE_DRAWTEXT_FILTER_AVAILABLE ? it : it.skip;

 interface NativeExecution {
  readonly outputPaths: readonly string[];
@@ -752,6 +763,33 @@ describeNative('native execution of structured command plans', () => {
      Number(probe(normalized.outputPaths[0]!).format?.duration)
    ).toBeCloseTo(1.6, 1);

+    const crossfaded = runNative(
+      buildNormalizedConcatPlan({
+        jobId: 'crossfade-concat-native',
+        sources: [
+          concatSource('first', 0, 'compatible-a.mp4', 128, 72),
+          concatSource('second', 1, 'compatible-b.mp4', 128, 72),
+        ],
+        targetExtension: 'mp4',
+        targetMuxer: 'mp4',
+        preset: preset('mp4-h264-balanced'),
+        width: 128,
+        height: 72,
+        frameRate: 10,
+        sampleRate: 16_000,
+        channelLayout: 'mono',
+        missingAudioPolicy: 'reject',
+        crossfadeSeconds: 0.2,
+      }),
+      {
+        first: fixture('compatible-a.mp4'),
+        second: fixture('compatible-b.mp4'),
+      }
+    );
+    expect(
+      Number(probe(crossfaded.outputPaths[0]!).format?.duration)
+    ).toBeCloseTo(1.8, 1);
+
    const videoOnly = join(suiteDirectory, 'compatible-video-only.mp4');
    nativeCommand(
      [
@@ -788,6 +826,7 @@ describeNative('native execution of structured command plans', () => {
        sampleRate: 16_000,
        channelLayout: 'mono',
        missingAudioPolicy: 'insert-silence',
+        crossfadeSeconds: 0.2,
      }),
      { first: fixture('compatible-a.mp4'), 'video-only': videoOnly }
    );
@@ -1185,8 +1224,80 @@ describeNative('native execution of structured command plans', () => {
      codec_name: 'png',
      width: 166,
    });
+
+    const sceneAnalysis = runNative(
+      buildSceneChangeAnalysisPlan({
+        jobId: 'scene-analysis-native',
+        source: media,
+        durationSeconds: 2,
+        threshold: 0.01,
+        maxFrames: 4,
+      }),
+      { media: mediaFile },
+      'info'
+    );
+    const sceneFrames = parseSceneChangeFrames(sceneAnalysis.stderr);
+    expect(sceneFrames.length).toBeGreaterThan(0);
+    const sceneSeries = runNative(
+      buildSceneThumbnailSeriesPlan({
+        jobId: 'scene-series-native',
+        source: media,
+        durationSeconds: 2,
+        frames: sceneFrames,
+        size: { width: 80 },
+        format: 'png',
+      }),
+      { media: mediaFile }
+    );
+    expect(sceneSeries.outputPaths).toHaveLength(sceneFrames.length);
+
+    const sceneSheet = runNative(
+      buildContactSheetPlan({
+        jobId: 'scene-contact-sheet-native',
+        source: media,
+        durationSeconds: 2,
+        frameCount: sceneFrames.length,
+        rows: 1,
+        columns: sceneFrames.length,
+        cellWidth: 80,
+        spacing: 2,
+        sceneFrames,
+        format: 'png',
+      }),
+      { media: mediaFile }
+    );
+    expect(statSync(sceneSheet.outputPaths[0]!).size).toBeGreaterThan(500);
  }, 120_000);

+  itNativeDrawtext(
+    'executes contact-sheet labels with the reviewed bundled font',
+    () => {
+      const media = source('media', 0, 'pattern-av.mp4');
+      const labeledSheet = runNative(
+        buildContactSheetPlan({
+          jobId: 'labeled-contact-sheet-native',
+          source: media,
+          durationSeconds: 2,
+          frameCount: 2,
+          rows: 1,
+          columns: 2,
+          cellWidth: 120,
+          timestampLabels: true,
+          sourceLabel: true,
+          drawtextAvailable: true,
+          font: source('font', 1, 'DejaVuSans.ttf'),
+          format: 'png',
+        }),
+        {
+          media: fixture('pattern-av.mp4'),
+          font: resolve(process.cwd(), 'public/fonts/DejaVuSans.ttf'),
+        }
+      );
+      expect(statSync(labeledSheet.outputPaths[0]!).size).toBeGreaterThan(500);
+    },
+    120_000
+  );
+
  it('executes a transformed, faded, normalized sequential timeline', () => {
    const execution = runNative(
      buildTimelineExportPlan({
--- a/tests/unit/advanced-operations.test.tsx
+++ b/tests/unit/advanced-operations.test.tsx
@@ -283,6 +283,72 @@ describe('AdvancedOperations', () => {
    );
  });

+  it('emits bounded scene analysis settings for series and contact sheets', async () => {
+    const user = userEvent.setup();
+    const onThumbnailSeries = vi.fn();
+    const onContactSheet = vi.fn();
+    render(
+      <AdvancedOperations
+        source={SOURCE}
+        availability={capabilities(
+          'thumbnail-series',
+          'contact-sheet',
+          'scene-change-analysis',
+          'contact-sheet-labels'
+        )}
+        imageFormatAvailability={{ jpeg: AVAILABLE }}
+        onThumbnailSeries={onThumbnailSeries}
+        onContactSheet={onContactSheet}
+      />
+    );
+
+    await user.click(
+      screen.getByRole('tab', {
+        name: 'Thumbnails and contact sheets',
+      })
+    );
+    const selectionFields = screen.getAllByLabelText('Frame selection');
+    await user.selectOptions(selectionFields[0]!, 'scene-changes');
+    await user.clear(screen.getByLabelText('Scene sensitivity threshold'));
+    await user.type(
+      screen.getByLabelText('Scene sensitivity threshold'),
+      '0.42'
+    );
+    await user.click(
+      screen.getByRole('button', { name: 'Generate thumbnail series' })
+    );
+    await waitFor(() =>
+      expect(onThumbnailSeries).toHaveBeenCalledWith({
+        distribution: {
+          type: 'scene-changes',
+          count: 12,
+          threshold: 0.42,
+        },
+        width: 480,
+        format: 'jpeg',
+        quality: 85,
+      })
+    );
+
+    await user.selectOptions(selectionFields[1]!, 'scene-changes');
+    await user.clear(screen.getByLabelText('Contact-sheet scene threshold'));
+    await user.type(
+      screen.getByLabelText('Contact-sheet scene threshold'),
+      '0.3'
+    );
+    await user.click(
+      screen.getByRole('button', { name: 'Generate contact sheet' })
+    );
+    await waitFor(() =>
+      expect(onContactSheet).toHaveBeenCalledWith(
+        expect.objectContaining({
+          frameCount: 12,
+          selection: { type: 'scene-changes', threshold: 0.3 },
+        })
+      )
+    );
+  });
+
  it('classifies bitmap subtitles conservatively before enabling extraction', async () => {
    const user = userEvent.setup();
    const onSubtitleAction = vi.fn();
--- a/tests/unit/bundled-font-assets.test.ts
+++ b/tests/unit/bundled-font-assets.test.ts
@@ -0,0 +1,31 @@
+import { createHash } from 'node:crypto';
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import { describe, expect, it } from 'vitest';
+import { BUNDLED_CONTACT_SHEET_FONT } from '../../src/assets/bundled-font';
+
+describe('bundled contact-sheet font', () => {
+  it('matches its reviewed byte identity and ships the embedded licence', () => {
+    const bytes = readFileSync(
+      resolve(
+        process.cwd(),
+        'public/fonts',
+        BUNDLED_CONTACT_SHEET_FONT.fileName
+      )
+    );
+    expect(bytes.byteLength).toBe(BUNDLED_CONTACT_SHEET_FONT.byteLength);
+    expect(createHash('sha256').update(bytes).digest('hex')).toBe(
+      BUNDLED_CONTACT_SHEET_FONT.sha256
+    );
+
+    const licence = readFileSync(
+      resolve(process.cwd(), BUNDLED_CONTACT_SHEET_FONT.licenseFile),
+      'utf8'
+    );
+    expect(licence).toContain('Bitstream Vera Fonts Copyright');
+    expect(licence).toContain('Arev Fonts Copyright');
+    expect(licence).toContain(
+      'The above copyright and trademark notices and this permission notice'
+    );
+  });
+});
--- a/tests/unit/commands-advanced.test.ts
+++ b/tests/unit/commands-advanced.test.ts
@@ -9,6 +9,8 @@ import {
  buildPeakAnalysisPlan,
  buildPeakNormalizationFilter,
  buildPeakNormalizationPlan,
+  buildSceneChangeAnalysisPlan,
+  buildSceneThumbnailSeriesPlan,
  buildSubtitleBurnPlan,
  buildSubtitleExtractionPlan,
  buildSubtitleMuxPlan,
@@ -25,6 +27,7 @@ import {
  parseChapterJson,
  parseLoudnessMeasurement,
  parsePeakMeasurement,
+  parseSceneChangeFrames,
  parseMetadataJson,
  resolveThumbnailTimes,
  serializeChapterJson,
@@ -360,6 +363,65 @@ describe('thumbnail and contact sheet plans', () => {
    expect(plan.args.some((value) => value.includes('%03d'))).toBe(false);
  });

+  it('analyzes a bounded number of scene changes and parses exact timestamps', () => {
+    const plan = buildSceneChangeAnalysisPlan({
+      jobId: 'scenes',
+      source: SOURCE,
+      durationSeconds: 10,
+      threshold: 0.35,
+      maxFrames: 12,
+    });
+    expect(plan.outputs).toEqual([]);
+    expect(plan.args).toEqual(
+      expect.arrayContaining([
+        "select='gt(scene\\,0.35)',showinfo",
+        '-frames:v',
+        '12',
+        '-f',
+        'null',
+      ])
+    );
+    expect(plan.requiredCapabilities.filters).toEqual(['select', 'showinfo']);
+    expect(
+      parseSceneChangeFrames(`
+[Parsed_showinfo_1 @ 0x1] n:   0 pts:   4096 pts_time:0.25 duration:512
+n:   1 pts:  16384 pts_time:1 duration:512
+[Parsed_showinfo_1 @ 0x1] n:   2 pts:  16384 pts_time:1 duration:512
+invalid showinfo n: 3 pts: nope pts_time:2
+`)
+    ).toEqual([
+      { pts: 4096, timeSeconds: 0.25 },
+      { pts: 16384, timeSeconds: 1 },
+    ]);
+  });
+
+  it('builds exact scene-selected thumbnails from analyzed PTS values', () => {
+    const plan = buildSceneThumbnailSeriesPlan({
+      jobId: 'scene-thumbs',
+      source: SOURCE,
+      durationSeconds: 10,
+      frames: [
+        { pts: 4096, timeSeconds: 0.25 },
+        { pts: 16384, timeSeconds: 1 },
+      ],
+      format: 'png',
+      size: { width: 320 },
+    });
+    expect(plan.outputs.map((output) => output.fileName)).toEqual([
+      'source-thumbnail-001-250ms.png',
+      'source-thumbnail-002-1000ms.png',
+    ]);
+    expect(plan.args.join(' ')).toContain(
+      "select='eq(pts\\,4096)+eq(pts\\,16384)',split=2"
+    );
+    expect(plan.requiredCapabilities.filters).toEqual([
+      'select',
+      'split',
+      'setpts',
+      'scale',
+    ]);
+  });
+
  it('degrades contact-sheet labels when drawtext is unavailable', () => {
    const plan = buildContactSheetPlan({
      jobId: 'sheet',
@@ -381,6 +443,49 @@ describe('thumbnail and contact sheet plans', () => {
    );
    expect(plan.requiredCapabilities.filters).not.toContain('drawtext');
  });
+
+  it('uses a mounted reviewed font and exact scene frames for labels', () => {
+    const plan = buildContactSheetPlan({
+      jobId: 'scene-sheet',
+      source: SOURCE,
+      durationSeconds: 10,
+      frameCount: 2,
+      rows: 1,
+      columns: 2,
+      cellWidth: 240,
+      timestampLabels: true,
+      sourceLabel: true,
+      format: 'jpeg',
+      drawtextAvailable: true,
+      font: {
+        id: 'bundled-font',
+        sourceIndex: 1,
+        fileName: 'DejaVuSans.ttf',
+      },
+      sceneFrames: [
+        { pts: 4096, timeSeconds: 0.25 },
+        { pts: 16384, timeSeconds: 1 },
+      ],
+    });
+    expect(plan.inputs[1]).toMatchObject({
+      kind: 'font',
+      sourceIndex: 1,
+    });
+    expect(plan.args.join(' ')).toContain(
+      "select='eq(pts\\,4096)+eq(pts\\,16384)'"
+    );
+    expect(plan.args.join(' ')).toContain(
+      "drawtext=fontfile='/input/job-scene-sheet/source-1.ttf'"
+    );
+    expect(plan.args.join(' ')).toContain('nb_frames=2');
+    expect(plan.requiredCapabilities.filters).toEqual([
+      'select',
+      'scale',
+      'setpts',
+      'tile',
+      'drawtext',
+    ]);
+  });
 });

 describe('composed visual operations', () => {
--- a/tests/unit/commands.test.ts
+++ b/tests/unit/commands.test.ts
@@ -2,6 +2,7 @@ import { describe, expect, it } from 'vitest';
 import {
  buildConvertPlan,
  buildFastConcatPlan,
+  buildNormalizedConcatPlan,
  buildPreviewProxyPlan,
  buildRemuxPlan,
  buildSplitPlan,
@@ -276,6 +277,64 @@ describe('concat and transform validation', () => {
    expect(plan.expectedDurationSeconds).toBe(5);
  });

+  it('builds bounded chained audio/video crossfades for normalized concat', () => {
+    const preset = findBuiltInPreset('mp4-h264-balanced');
+    const sources = [
+      { ...SOURCES[0]!, durationSeconds: 4 },
+      { ...SOURCES[1]!, durationSeconds: 5 },
+      {
+        ...SOURCES[1]!,
+        id: 'three',
+        sourceIndex: 2,
+        fileName: 'three.mp4',
+        durationSeconds: 3,
+      },
+    ];
+    const plan = buildNormalizedConcatPlan({
+      jobId: 'crossfade',
+      sources,
+      targetExtension: 'mp4',
+      targetMuxer: 'mp4',
+      preset: preset!,
+      width: 640,
+      height: 360,
+      frameRate: 25,
+      sampleRate: 48_000,
+      channelLayout: 'stereo',
+      missingAudioPolicy: 'reject',
+      subtitlePolicy: 'reject',
+      crossfadeSeconds: 0.5,
+    });
+    const graph = plan.args[plan.args.indexOf('-filter_complex') + 1] ?? '';
+    expect(graph).toContain(
+      '[v0][v1]xfade=transition=fade:duration=0.5:offset=3.5[vxf1]'
+    );
+    expect(graph).toContain(
+      '[vxf1][v2]xfade=transition=fade:duration=0.5:offset=8[vout]'
+    );
+    expect(graph).toContain('[a0][a1]acrossfade=d=0.5:c1=tri:c2=tri[axf1]');
+    expect(graph).not.toContain('concat=n=3');
+    expect(plan.expectedDurationSeconds).toBe(11);
+    expect(plan.requiredCapabilities.filters).toEqual(
+      expect.arrayContaining(['xfade', 'acrossfade'])
+    );
+    expect(() =>
+      buildNormalizedConcatPlan({
+        jobId: 'too-long-crossfade',
+        sources: SOURCES,
+        targetExtension: 'mp4',
+        targetMuxer: 'mp4',
+        preset: preset!,
+        width: 640,
+        height: 360,
+        frameRate: 25,
+        missingAudioPolicy: 'reject',
+        subtitlePolicy: 'reject',
+        crossfadeSeconds: 2.5,
+      })
+    ).toThrow(/Clip 1 needs at least/iu);
+  });
+
  it('corrects crop to even bounds and calculates aspect-preserving resize', () => {
    expect(
      validateCrop({
--- a/tests/unit/components/help-dialog.test.tsx
+++ b/tests/unit/components/help-dialog.test.tsx
@@ -16,7 +16,9 @@ describe('HelpDialog', () => {
    ).toBeInTheDocument();
    expect(screen.getByText('n5.1.4')).toBeInTheDocument();
    expect(screen.getByText('0.12.15')).toBeInTheDocument();
-    expect(screen.getByText('0.12.10 · ST & MT')).toBeInTheDocument();
+    expect(
+      screen.getByText('0.12.10-reviewed-stack5m.1 · ST & MT')
+    ).toBeInTheDocument();
    expect(
      screen.getByText(/copyright © 2026 Albrecht Degering/i)
    ).toBeInTheDocument();
@@ -29,6 +31,9 @@ describe('HelpDialog', () => {
    expect(
      screen.getByRole('link', { name: 'GPL text', hidden: true })
    ).toHaveAttribute('href', expect.stringContaining('GPL-2.0-or-later'));
+    expect(
+      screen.getByRole('link', { name: 'Font licence', hidden: true })
+    ).toHaveAttribute('href', expect.stringContaining('DEJAVU_FONTS'));
    expect(
      screen.getByRole('link', {
        name: 'Complete inventory',
--- a/tests/unit/components/media-preview.test.tsx
+++ b/tests/unit/components/media-preview.test.tsx
@@ -26,6 +26,41 @@ afterEach(() => {
 });

 describe('MediaPreview', () => {
+  it('starts declared local video playback while inspection continues and preserves the element', () => {
+    const probingAsset: ImportedMediaAsset = {
+      id: 'asset-probing-video',
+      file: new File(['video'], 'lecture.mp4', {
+        type: 'application/octet-stream',
+      }),
+      objectUrl: 'blob:probing-video',
+      phase: 'probing',
+    };
+    const { container, rerender } = render(
+      <MediaPreview asset={probingAsset} />
+    );
+
+    const progressiveVideo = requiredElement(container.querySelector('video'));
+    expect(progressiveVideo).toHaveAttribute('src', probingAsset.objectUrl);
+    expect(
+      screen.getByText(
+        'Local source preview · Media inspection continues in the background.'
+      )
+    ).toBeVisible();
+
+    rerender(
+      <MediaPreview
+        asset={{
+          ...videoAsset(),
+          id: probingAsset.id,
+          file: probingAsset.file,
+          objectUrl: probingAsset.objectUrl,
+        }}
+      />
+    );
+
+    expect(container.querySelector('video')).toBe(progressiveVideo);
+  });
+
  it('offers bounded configurable proxy settings after playback fails', async () => {
    const user = userEvent.setup();
    const onCreateProxy = vi.fn();
--- a/tests/unit/components/quick-convert.test.tsx
+++ b/tests/unit/components/quick-convert.test.tsx
@@ -138,6 +138,28 @@ describe('QuickConvert', () => {
    ).toBeDisabled();
  });

+  it('enables Opus after the reviewed core passed both regression modes', () => {
+    const engineState: EngineState = {
+      status: 'ready',
+      mode: 'single-thread',
+      capabilities: {
+        ...capabilities(['mp4', 'opus']),
+        encoders: new Set(['libx264', 'aac', 'libopus']),
+      },
+    };
+
+    render(
+      <QuickConvert
+        asset={createAsset('asset-a', 'source-a.mp4')}
+        engineState={engineState}
+        busy={false}
+        onExport={vi.fn()}
+      />
+    );
+
+    expect(screen.getByRole('option', { name: 'Opus' })).toBeEnabled();
+  });
+
  it('exposes a validated user preset and returns it unchanged on export', async () => {
    const user = userEvent.setup();
    const onExport = vi.fn<(configuration: QuickExportConfiguration) => void>();
--- a/tests/unit/components/structural-operations.test.tsx
+++ b/tests/unit/components/structural-operations.test.tsx
@@ -274,6 +274,7 @@ describe('StructuralOperations', () => {
        presetId: 'video-ready',
        missingAudioPolicy: 'insert-silence',
        subtitlePolicy: 'reject',
+        crossfadeSeconds: 0,
      })
    );
  });
@@ -328,6 +329,55 @@ describe('StructuralOperations', () => {
        presetId: 'video-ready',
        missingAudioPolicy: 'insert-silence',
        subtitlePolicy: 'drop-all',
+        crossfadeSeconds: 0,
+      })
+    );
+  });
+
+  it('emits a bounded crossfade only after its filters are verified', async () => {
+    const user = userEvent.setup();
+    const onConcat = vi.fn();
+    render(
+      <StructuralOperations
+        timeline={{
+          ...TIMELINE,
+          clips: TIMELINE.clips.map((clip) => ({
+            ...clip,
+            durationSeconds: 3,
+          })),
+        }}
+        exportPresets={PRESETS}
+        availability={capabilities('concat-normalized', 'concat-crossfade')}
+        onConcat={onConcat}
+      />
+    );
+
+    await user.click(
+      screen.getByRole('radio', { name: /Normalized re-encode/iu })
+    );
+    await user.selectOptions(
+      screen.getByLabelText('Normalized concat preset'),
+      'video-ready'
+    );
+    await user.click(screen.getByRole('radio', { name: /Insert silence/iu }));
+    await user.click(
+      screen.getByRole('radio', { name: /Reject subtitle input/iu })
+    );
+    await user.clear(screen.getByLabelText(/^Crossfade duration/iu));
+    await user.type(screen.getByLabelText(/^Crossfade duration/iu), '0.5');
+    await user.click(
+      screen.getByRole('button', { name: 'Export normalized concat' })
+    );
+
+    await waitFor(() =>
+      expect(onConcat).toHaveBeenCalledWith({
+        operation: 'concat',
+        mode: 'normalized',
+        clipIds: ['clip-a', 'clip-b'],
+        presetId: 'video-ready',
+        missingAudioPolicy: 'insert-silence',
+        subtitlePolicy: 'reject',
+        crossfadeSeconds: 0.5,
      })
    );
  });
--- a/tests/unit/ffmpeg-engine-arguments.test.ts
+++ b/tests/unit/ffmpeg-engine-arguments.test.ts
@@ -1,11 +1,15 @@
-import { describe, expect, it } from 'vitest';
+import { describe, expect, it, vi } from 'vitest';
 import {
  DEFAULT_JOB_TIMEOUT_MILLISECONDS,
+  EngineManager,
  MAX_CONTACT_SHEETS_PER_ENGINE,
  MAX_EXECUTIONS_PER_ENGINE,
+  MAX_PROBE_TIMEOUT_MILLISECONDS,
+  MIN_PROBE_TIMEOUT_MILLISECONDS,
  MULTITHREAD_CODEC_THREAD_LIMIT,
  engineJobTimeoutMilliseconds,
  prepareEngineArguments,
+  probeTimeoutMilliseconds,
  shouldRecycleExecutionCore,
 } from '../../src/ffmpeg/EngineManager';

@@ -90,6 +94,39 @@ describe('engineJobTimeoutMilliseconds', () => {
  });
 });

+describe('probeTimeoutMilliseconds', () => {
+  it('keeps small probes responsive, scales real media, and caps the watchdog', () => {
+    expect(probeTimeoutMilliseconds(34_057)).toBe(
+      MIN_PROBE_TIMEOUT_MILLISECONDS
+    );
+    expect(probeTimeoutMilliseconds(153_019_068)).toBe(72_966);
+    expect(probeTimeoutMilliseconds(2 * 1024 * 1024 * 1024)).toBe(
+      MAX_PROBE_TIMEOUT_MILLISECONDS
+    );
+  });
+
+  it('rejects an already-cancelled probe before loading an engine', async () => {
+    const factory = vi.fn(async () => {
+      throw new Error('The engine factory must not be called.');
+    });
+    const manager = new EngineManager(factory);
+    const controller = new AbortController();
+    controller.abort();
+
+    await expect(
+      manager.probe(
+        new File(['media'], 'cancelled.mp4', { type: 'video/mp4' }),
+        undefined,
+        controller.signal
+      )
+    ).rejects.toMatchObject({
+      code: 'cancelled',
+      message: 'The media probe was cancelled.',
+    });
+    expect(factory).not.toHaveBeenCalled();
+  });
+});
+
 describe('execution core recycling policy', () => {
  it('refreshes only after the bounded idle-core job budget is exhausted', () => {
    expect(shouldRecycleExecutionCore(MAX_EXECUTIONS_PER_ENGINE - 1)).toBe(
--- a/tests/unit/ffmpeg-utils.test.ts
+++ b/tests/unit/ffmpeg-utils.test.ts
@@ -20,8 +20,12 @@ describe('FFmpeg runtime utilities', () => {
      'multithread',
      (path) => `https://tools.example/deep/${path}`
    );
-    expect(mt.coreURL).toContain('/0.12.10/mt/ffmpeg-core.js');
-    expect(mt.workerURL).toContain('/0.12.10/mt/ffmpeg-core.worker.js');
+    expect(mt.coreURL).toContain(
+      '/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.js'
+    );
+    expect(mt.workerURL).toContain(
+      '/0.12.10-reviewed-stack5m.1/mt/ffmpeg-core.worker.js'
+    );
  });

  it('clamps experimental progress and removes invalid numbers', () => {
--- a/tests/unit/release-package.test.mjs
+++ b/tests/unit/release-package.test.mjs
@@ -165,30 +165,30 @@ describe('licence release gate', () => {
 describe('release checksum', () => {
  it('formats and parses the portable sidecar form', () => {
    const digest = 'a'.repeat(64);
-    const line = checksumLine(digest, 'av-tools-0.1.0.zip');
-    expect(line).toBe(`${digest}  av-tools-0.1.0.zip\n`);
+    const line = checksumLine(digest, 'av-tools-0.2.0.zip');
+    expect(line).toBe(`${digest}  av-tools-0.2.0.zip\n`);
    expect(parseChecksumLine(line)).toEqual({
-      archiveName: 'av-tools-0.1.0.zip',
+      archiveName: 'av-tools-0.2.0.zip',
      digest,
    });
  });

  it('writes and verifies a checksum sidecar', async () => {
    const directory = await temporaryDirectory();
-    const archive = path.join(directory, 'av-tools-0.1.0.zip');
+    const archive = path.join(directory, 'av-tools-0.2.0.zip');
    await writeFile(archive, 'deterministic bytes');
    const result = await writeChecksum(archive);
    expect(await verifyChecksum(archive, result.sidecarPath)).toBe(
      result.digest
    );
    expect(await readFile(result.sidecarPath, 'utf8')).toContain(
-      '  av-tools-0.1.0.zip'
+      '  av-tools-0.2.0.zip'
    );
  });

  it('rejects checksum mismatches', async () => {
    const directory = await temporaryDirectory();
-    const archive = path.join(directory, 'av-tools-0.1.0.zip');
+    const archive = path.join(directory, 'av-tools-0.2.0.zip');
    const sidecar = `${archive}.sha256`;
    await writeFile(archive, 'changed');
    await mkdir(path.dirname(sidecar), { recursive: true });
@@ -207,7 +207,7 @@ describe('portal assembly smoke validation', () => {
    add_header Cross-Origin-Resource-Policy "same-origin" always;
    add_header Content-Security-Policy "default-src 'self'; script-src 'self' 'wasm-unsafe-eval'; worker-src 'self' blob:; media-src 'self' blob:;" always;
    types { application/wasm wasm; }
-    # vendor/ffmpeg/0.12.10
+    "~^/apps/av/vendor/ffmpeg/0.12.10-reviewed-stack5m.1/(?:st|mt)/ffmpeg-core\\.(?:js|wasm)$" "public, max-age=31536000, immutable";
  `;

  it('accepts the required isolation, CSP and MIME profile', () => {
@@ -226,6 +226,15 @@ describe('portal assembly smoke validation', () => {
    );
  });

+  it('does not mistake a plain-semver cache rule for reviewed-build coverage', () => {
+    const inspection = inspectPortalHeaders(
+      isolatedHeaders.replace('0.12.10-reviewed-stack5m.1', '0.12.10')
+    );
+    expect(inspection.warnings).toContainEqual(
+      expect.stringMatching(/reviewed FFmpeg build/u)
+    );
+  });
+
  it('parses only explicit smoke overrides and paths', () => {
    const parsed = parsePortalArguments(
      [
--- a/tests/unit/source-inspection-registry.test.ts
+++ b/tests/unit/source-inspection-registry.test.ts
@@ -0,0 +1,52 @@
+import { describe, expect, it } from 'vitest';
+
+import { SourceInspectionRegistry } from '../../src/app/source-inspection-registry';
+
+describe('SourceInspectionRegistry', () => {
+  it('invalidates queued work synchronously and does not request cancellation', () => {
+    const registry = new SourceInspectionRegistry();
+    const token = registry.register('queued');
+
+    expect(registry.remove('queued')).toBe(false);
+    expect(registry.isCurrent(token)).toBe(false);
+    expect(registry.activate(token)).toBe(false);
+    expect(token.signal.aborted).toBe(true);
+  });
+
+  it('requests cancellation for the active asset and rejects its late result', () => {
+    const registry = new SourceInspectionRegistry();
+    const token = registry.register('active');
+
+    expect(registry.activate(token)).toBe(true);
+    expect(registry.remove('active')).toBe(true);
+    expect(registry.isCurrent(token)).toBe(false);
+    expect(token.signal.aborted).toBe(true);
+    registry.finish(token);
+    expect(registry.remove('active')).toBe(false);
+  });
+
+  it('does not let a late generation overwrite a replacement with the same ID', () => {
+    const registry = new SourceInspectionRegistry();
+    const stale = registry.register('reattached');
+    expect(registry.activate(stale)).toBe(true);
+
+    const replacement = registry.register('reattached');
+    expect(registry.isCurrent(stale)).toBe(false);
+    expect(registry.isCurrent(replacement)).toBe(true);
+    expect(stale.signal.aborted).toBe(true);
+    expect(replacement.signal.aborted).toBe(false);
+    registry.finish(stale);
+    expect(registry.activate(replacement)).toBe(true);
+  });
+
+  it('invalidates all queued work and identifies an active probe on clear', () => {
+    const registry = new SourceInspectionRegistry();
+    const active = registry.register('active');
+    const queued = registry.register('queued');
+    registry.activate(active);
+
+    expect(registry.clear()).toBe(true);
+    expect(registry.isCurrent(active)).toBe(false);
+    expect(registry.isCurrent(queued)).toBe(false);
+  });
+});
--- a/vendor/ffmpeg-core-0.12.10-reviewed-stack5m.1.zip
+++ b/vendor/ffmpeg-core-0.12.10-reviewed-stack5m.1.zip
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -24,6 +24,11 @@ export default defineConfig({
    setupFiles: './src/test/setup.ts',
    css: true,
    restoreMocks: true,
-    exclude: ['tests/browser/**', 'node_modules/**', 'dist/**'],
+    exclude: [
+      'tests/browser/**',
+      'node_modules/**',
+      'dist/**',
+      '.core-build/**',
+    ],
  },
 });