feat: export as MP4 (karaoke video) for MP4 uploads and YouTube - #226
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Add an MP4 export that muxes the current mixer state (e.g. vocals muted)
with the source video, producing a karaoke-style video.
Backend:
- Preserve a silent video.mp4 from .mp4 uploads (stream-copy, no re-encode).
- YouTube jobs do a best-effort video-only download (H.264/avc1, <=720p)
to video.mp4, decoupled from the audio source so failures degrade to
audio-only. New STEMDECK_VIDEO_MAX_HEIGHT config.
- GET /api/jobs/{id}/video.mp4 streams a fragmented MP4: the amix audio
graph encoded as AAC, video stream-copied.
- has_video flag on Job, surfaced in state and persisted to metadata.
Frontend:
- MP4 added as a fourth export format (WAV/MP3/FLAC/MP4), shown only for
jobs with a preserved video track. In MP4 mode, Export Mix produces the
karaoke video and the audio-only Stems/Region rows are hidden.
SoundCloud and plain audio uploads are audio-only (no MP4 option).
added 2 commits
June 25, 2026 22:38
Linux no longer requires `sudo apt install ffmpeg`. The desktop shell now downloads a static FFmpeg build into the user data dir on first launch (like Windows/macOS), falling back to a system ffmpeg on PATH when present. This also fixes Demucs failing to decode compressed sources, since the download lands in data_dir/ffmpeg which config.json already adds to PATH. - ensure_ffmpeg: prefer a system ffmpeg, else download_linux_ffmpeg. - download_linux_ffmpeg: fetch the .tar.xz, extract with system tar, copy ffmpeg + ffprobe into data_dir/ffmpeg. STEMDECK_FFMPEG_URL overrides. - Widen download_file and make_executable from macos to unix so Linux reuses them. - Not bundled in the tarball, so we don't redistribute FFmpeg. - Update Linux README/notices/packaging comment to drop the ffmpeg apt step.
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Closes #219.
What
Adds an MP4 export that muxes the current mixer state (e.g. vocals muted) with the source video, producing a karaoke-style video the user can sing along to.
.mp4Backend
.mp4uploads — extract a silentvideo.mp4(stream-copy, no re-encode) before the source is transcoded for Demucs.bestvideo[vcodec^=avc1], ≤STEMDECK_VIDEO_MAX_HEIGHT/720p) tovideo.mp4. The audio source download is untouched; any video failure degrades gracefully to audio-only. H.264 is preferred so the export plays everywhere (avoids AV1, which Safari/iOS can't decode).GET /api/jobs/{id}/video.mp4?stems=&gains=— streams a fragmented MP4: the sameamixaudio graph as the existing mixdown (encoded AAC) with the video stream-copied. 404 when the job has no video.has_videoflag onJob, surfaced in state and persisted tometadata.json.Frontend
Tests
_extract_video_trackpreserves video from an.mp4and skips audio-only.mp4.Notes
Also in this PR — Linux FFmpeg
Linux no longer needs
sudo apt install ffmpeg. The desktop shell downloads a static FFmpeg on first launch (like Windows/macOS), falling back to a systemffmpegon PATH when present. Not bundled in the tarball, so we do not redistribute FFmpeg. Also fixes Demucs failing on compressed sources in source/dev runs.download_file/make_executablefrom macos to unix for reuse.