144 lines
6.1 KiB
Markdown
144 lines
6.1 KiB
Markdown
# FFmpeg WebAssembly build record
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av-tools ships the published ESM assets from `@ffmpeg/core` and
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`@ffmpeg/core-mt` **0.12.10**. The browser wrapper is `@ffmpeg/ffmpeg`
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**0.12.15** and helpers are `@ffmpeg/util` **0.12.2**. All versions are exact,
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not ranges.
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## Underlying build
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The matching ffmpeg.wasm upstream release is `v12.15` at
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`71aa99d37c02a7b4c435275ca9ef50e612f6efa1`. Its Dockerfile selects:
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- FFmpeg **n5.1.4** (libavcodec 59.37.100);
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- Emscripten SDK **3.1.40**;
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- production `-O3 -msimd128`;
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- pthread flags for the MT build and explicit thread disabling for ST.
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The build configuration embedded in both copied WASM files is:
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```text
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--target-os=none
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--arch=x86_32
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--enable-cross-compile
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--disable-asm
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--disable-stripping
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--disable-programs
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--disable-doc
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--disable-debug
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--disable-runtime-cpudetect
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--disable-autodetect
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--nm=emnm
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--ar=emar
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--ranlib=emranlib
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--cc=emcc
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--cxx=em++
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--objcc=emcc
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--dep-cc=emcc
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--extra-cflags='-I/opt/include -O3 -msimd128'
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--extra-cxxflags='-I/opt/include -O3 -msimd128'
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--enable-gpl
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--enable-libx264
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--enable-libx265
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--enable-libvpx
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--enable-libmp3lame
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--enable-libtheora
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--enable-libvorbis
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--enable-libopus
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--enable-zlib
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--enable-libwebp
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--enable-libfreetype
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--enable-libfribidi
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--enable-libass
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--enable-libzimg
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```
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The ST string also has `--disable-pthreads --disable-w32threads
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--disable-os2threads`; the MT build supplies Emscripten pthread flags instead.
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At runtime the application executes `-version`, `-buildconf`, `-formats`,
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`-codecs`, `-encoders` and `-filters` sequentially. Presets are enabled only
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when the active core reports every required muxer, encoder and filter. Build
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flags alone are not treated as a capability guarantee.
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## External libraries
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The upstream build references x264 `4-cores`, x265 3.4, libvpx v1.13.1, LAME
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`master`, Ogg v1.3.4, Theora v1.1.1, Opus v1.3.1, Vorbis v1.3.3, zlib v1.2.11,
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libwebp v1.3.2, FreeType VER-2-10-4, FriBidi v1.0.9, HarfBuzz 5.2.0, libass
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0.15.0 and zimg release-3.0.5. These resolve to x264
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`33cac6b77d5b9259c552156013a817ab23119612`, x265
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`2bb5520e9596f361bf0ed81b3b8da0d7fd999069` and LAME
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`2badea1974ae36cb8312afe99cff1e6b3b5decee`. All three commits predate the
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ffmpeg.wasm v12.15 release; the branch-based x264/LAME commits remain the
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respective branch tips. `SOURCE.md` records retrieval commands.
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## Shipped files
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| Mode | File | Bytes | SHA-256 |
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| ---- | -------------------------- | -------: | ------------------------------------------------------------------ |
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| ST | `st/ffmpeg-core.js` | 111804 | `67a48f11645f85439f3fde4f2119042c16b374b910206b7a7a24f342e28dcae3` |
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| ST | `st/ffmpeg-core.wasm` | 32232419 | `9f57947a5bd530d8f00c5b3f2cb2a3492faa7e5d823315342d6a8656d0a6b7b7` |
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| MT | `mt/ffmpeg-core.js` | 128947 | `270a2e6ff945e173238610669a3f7132df5f9c52698a9bf708cf5c2ab6bda0de` |
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| MT | `mt/ffmpeg-core.wasm` | 32718323 | `be2c97605366b78f3f13e21b52e81a55a79e1f29c133b03a68ec187b1a2ec41a` |
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| MT | `mt/ffmpeg-core.worker.js` | 2115 | `f77898d631dc010b45c29c23cb4379c611a7d7b131bf591d08a656bb729a4ca3` |
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`npm run vendor:ffmpeg` copies these files from `node_modules` to
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`public/vendor/ffmpeg/0.12.10/`; `npm run vendor:verify` checks versions,
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sizes, paths and digests. Vite then copies them unchanged into `dist`. A normal
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production build performs no network download.
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## Multithread Chromium guardrail
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The pinned multithread core can stall in Chromium when FFmpeg lets codecs use
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the browser's full reported logical-core count. This is tracked upstream in
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[ffmpeg.wasm issue 654](https://github.com/ffmpegwasm/ffmpeg.wasm/issues/654).
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av-tools keeps the pthread core but adds `-threads 2` as an input and output
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codec option for MT jobs. ST arguments remain unchanged. A regular browser
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test performs an actual MT H.264/AAC conversion; loading the core alone is not
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accepted as functional evidence.
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Every execution also has a watchdog: an explicit shorter plan timeout wins;
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otherwise the timeout is at least two minutes, scales to thirty times the
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expected media duration, and is capped at the displayed four-hour product
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limit. Timeout is still a failure, not a successful partial export.
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## Long-session heap guardrail
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The pinned Emscripten core was observed to end a later heterogeneous browser
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workflow with a bare `Aborted()` even though the same command passed in a
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fresh core and all per-job virtual files had been removed. Its `tile` filter
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also aborted deterministically on a fourth consecutive contact sheet in local
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stress runs. av-tools therefore refreshes an idle core before its seventeenth
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media execution and before a fourth contact-sheet execution. Application queue
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state, sources and completed results remain outside the worker and are not
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discarded. A bare core abort also triggers recreation after cleanup so a
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manual or queued retry starts on a fresh instance.
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This is a conservative browser-memory guardrail, not a guarantee that sixteen
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large jobs or three large contact sheets fit in memory. Cancellation and
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failed filesystem-cleanup recovery continue to recreate the core immediately.
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## Opus regression risk
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Pinned core 0.12.10 predates upstream ffmpeg.wasm fixes associated with stack
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size and Opus zero-byte/out-of-bounds failures (including upstream issues
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`#591` and `#775`). Therefore:
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- decoder/encoder listing is not enough to certify Opus;
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- real ST and MT fixture encodes must produce a non-empty, re-probeable output;
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- the Opus audio and VP9/Opus presets must remain disabled with a diagnostic
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if that smoke fails;
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- a core upgrade requires new checksums, capability snapshots, legal review
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and regression tests.
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This is a known pinned-core risk, not a claim that every Opus job fails.
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## Licence consequence
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The core packages declare GPL-2.0-or-later and the actual build enables GPL and
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links external codecs. The wrapper/util are MIT. av-tools is
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GPL-3.0-or-later, and the distributed application must not be described as
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MIT-only. Publish the reviewed Corresponding Source and external notices with
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the binary release. See `LICENSE`, `LICENSES/`, `THIRD_PARTY_NOTICES.md` and
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`SOURCE.md`.
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