lab/ux

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agra 2531fdcb74 FFmpeg software H.264 decoder: opt-in via pubspec flag

- Gate buildFfmpegJni + jniLibs packaging on `ux: enable_ffmpeg` in the
  consuming app's pubspec (default off) -- no LGPL / H.264-patent
  exposure unless explicitly enabled
- appInfoBuilder generates kUxEnableFfmpeg from the same flag so apps
  register the FFmpeg LGPL notice eagerly, pubspec-only (no dart-define)
- Add registerFfmpegLicense() + bundled LGPL-2.1 text asset
- FFmpeg compliance docs (LICENSES-3RDPARTY.md, android/ffmpeg/README.md)
- Network video streaming: XVideoPlayerController.network

2026-06-15 20:30:07 +03:00

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ux — Third-Party Licenses & Compliance

ux can bundle one component with distribution obligations: FFmpeg, used as a software H.264 video decoder on Android. It is opt-in and disabled by default — only apps that enable it ship it and inherit the obligation:

ux:
  enable_ffmpeg: true

That pubspec flag is the single source of truth: Gradle reads it for the native build, and ux's build_runner builder generates a kUxEnableFfmpeg constant from it into the app's app_info.g.dart, which gates registerFfmpegLicense() at startup — so the in-app LGPL notice follows automatically, eagerly, with no --dart-define.

Apps that enable it need to (a) surface a license UI and (b) be able to honor the source offer below; apps that leave it disabled have no FFmpeg obligation (and the in-app notice never appears).

FFmpeg (LGPL-2.1) — Android only

What and where

Compiled from source into libffmpegJNI.so per ABI and loaded at runtime via System.loadLibrary — an ExoPlayer/Media3 fallback decode-only renderer. Not a pub/Dart dependency. iOS/macOS use AVFoundation → no FFmpeg, no obligation there.

Build wiring: android/ffmpeg/ — build_ffmpeg.sh, CMakeLists.txt, ffmpeg_jni.cc, README.md, LICENSE-FFMPEG.txt.
Attribution: lib/builder.dart generates a kUxEnableFfmpeg constant from the app's ux: enable_ffmpeg pubspec flag into app_info.g.dart; the app gates registerFfmpegLicense() on it at startup (if (kUxEnableFfmpeg) registerFfmpegLicense();). So a build with the flag off registers nothing, and an enabled build shows the notice eagerly. Idempotent.
Bundled LGPL text asset: assets/licenses/ffmpeg_LGPL-2.1.txt.

Versions (pinned)

FFmpeg release/6.0 (upstream git.ffmpeg.org)
Media3 1.9.2 (JNI/renderer skeleton)

License posture

LGPL v2.1, dynamic boundary (separate, replaceable .so) → no copyleft on the consuming app.
Built decode-only (H.264 decoder, no encoders) and WITHOUT --enable-gpl / --enable-nonfree → LGPL-only. See build_ffmpeg.sh.

How we comply (LGPL-2.1)

Attribution + license text — registered via registerFfmpegLicense(), shown in any consuming app's license UI. ✅
Corresponding source — we make the FFmpeg release/6.0 source plus the build/link scripts (build_ffmpeg.sh, CMakeLists.txt, ffmpeg_jni.cc) available on request for ≥3 years. This does NOT include the application's own source code — only the LGPL library and the scripts that compile/link it. Contact: alex@swipelab.co. → Each release: archive the matching FFmpeg source tarball + the scripts.
Relink right (LGPL §6) — libffmpegJNI.so is a standalone, user-rebuildable shared library; sources + script are here, so a modified FFmpeg can be rebuilt and swapped in. ✅
Do not taint — never add --enable-gpl / --enable-nonfree or GPL-only codecs (x264, x265, …).

Patent note (for legal — separate from copyright)

FFmpeg's H.264 decoder code is LGPL, but the H.264/AVC standard is patent-encumbered (Via LA pool, formerly MPEG-LA). We ship a software AVC decoder — a patent/commercial matter for counsel, not an open-source or store-policy issue. Exposure is limited to decode (no encoder shipped).

Release checklist

FFmpeg/Media3 tags unchanged, or doc + archived source updated if bumped.
Build still omits --enable-gpl / --enable-nonfree; decode-only.
registerFfmpegLicense() reachable (auto on video, or eager at startup).
FFmpeg release/6.0 source tarball + scripts archived for this version.

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