Fix CTS=0 in fragmented fMP4 with multiple tracks (#317)

mirror of https://github.com/arcodange-org/mediabunny.git synced 2026-09-27 02:43:48 +02:00

* Fix CTS=0 in fragmented fMP4 with multiple tracks

When muxing fragmented MP4 with both video and audio tracks,
compositionTimeOffset (CTS) was zero for all video samples, causing
B-frame content to display in decode order instead of presentation
order (visible judder).

Root cause: During finalize(), interleaveSamples(true) triggers
finalizeFragment() via the cross-track keyframe check in
addSampleToTrack. This writes the trun box before processTimestamps
has computed correct decodeTimestamp values, so CTS = PTS - DTS = 0.

Fix: Call processTimestamps() for all tracks at the start of
finalizeFragment(). This is safe because processTimestamps is a no-op
when the timestampProcessingQueue is empty.

Video-only fragmented muxing was unaffected because the single-track
case never triggers the cross-track keyframe check during
interleaveSamples.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* Fix the problem at the actual root

* Oopsie doopsie

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>
Co-authored-by: Vanilagy <[email protected]>

This commit is contained in:

Kyle Graehl

2026-03-06 09:56:53 +00:00

committed by

GitHub

co-authored by

Claude Opus 4.6

Vanilagy

parent 472dc113e3

commit 6a11a1302c

4 changed files with 55 additions and 13 deletions

									
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							chunked: true,

							chunkSize: 2**20

						});

						const outputFormat = new Mediabunny.Mp4OutputFormat({});

						const outputFormat = new Mediabunny.Mp4OutputFormat({fastStart: 'fragmented'});

						const button = document.createElement('button');

						button.textContent = 'Cancel';