Adds the ffmpeg-binary half of the resolution stack so the upcoming
WebRTC streaming transcoder (Fase 3.3) has a single point of entry.
Search order matches ResolveFFprobe so operators don't need to learn a
second mental model:
1. Explicit path (--ffmpeg flag / library.ffmpeg_path config)
2. FFMPEG_PATH env var
3. "ffmpeg" on PATH (system install)
4. Adjacent to the unarr executable (release tarball bundles it here —
this is the preferred path; see Fase 3.2 goreleaser changes)
5. Cache dir (sibling of the cached ffprobe binary)
6. Auto-download from ffbinaries.com (~70MB) as last resort
Includes:
- internal/library/mediainfo/ffmpeg.go — ResolveFFmpeg + actionable
Docker / non-Docker error messages
- internal/library/mediainfo/ffmpeg_download.go — DownloadFFmpeg, reuses
ffprobePlatformKey + ffprobeAPIClient + ffprobeDLClient + extractFromZip
helpers; bumps maxZipSize to 200MB (ffmpeg static is ~70-100MB)
- internal/config: LibraryConfig.FFmpegPath toml field for explicit paths
- 4 unit tests: explicit OK, explicit missing, env var, sibling cache path
Tarball bundling and the actual transcoding pipeline land in the next
two commits.
