A/V Muxer — Trailer Scoring v5
⚠ You opened this as a local file, so Export won't work here — browsers block the background worker ffmpeg needs on file:// pages. Launch with Run A-V Muxer.bat (in this folder) instead; it serves the tool from localhost, where Export works. Preview & the timeline are fine either way.

Drops video + audio, lines the score up on a timeline, and bakes them into one .mp4. The video is stream-copied — never re-encoded, so picture quality is untouched. Only the audio is trimmed / offset / stretched (pitch preserved) and re-encoded.
Everything runs in your browser and works fully offline — the ffmpeg engine is bundled with the tool (in ffmpeg/); nothing is uploaded and nothing is fetched from the internet.

1 · Load files

Video Drop .mp4 or click picture is never altered
Audio Drop score (.mp3 / .wav / .m4a) or click trim · offset · stretch

2 · Preview

0.00 / 0.00s

3 · Timeline — drag block = move · side handles = trim in/out · stretch below

load a video
Video (locked)
clipped ✂
where in the score it starts
everything after is clipped
video time the audio begins
stretches/squishes the slice
Speed 1.000× natural · pitch preserved

4 · Export