Phase A captured raw .h264 streams but left them as non-playable elementary
streams. Phase B adds automatic muxing: when a video burst closes, the raw
.h264 is remuxed to a self-contained MP4 via `ffmpeg -c copy` (no re-encode,
fast) with `+faststart`, waits for the write stream to fully flush first so the
mux never reads a truncated tail, and deletes the raw .h264 on success (keeping
it on failure). Output: <RECORDINGS_DIR>/<uid>/video-<ssrc>-<ts>.mp4.
muxToMp4 is exported + covered by a real-ffmpeg vitest (tests/videoReceiver.test.ts):
generates a tiny baseline h264, remuxes, asserts mp4 exists/non-empty & raw deleted
(also the 5 depacketizer tests). Full gateway suite 170/170 green, tsc + biome clean.
asepharyana
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