FFmpeg

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Files

Zhao Zhili 56cf1c084d avformat/movenc: Fix flush fragment

The follow cmd output corrupted file before the patch:

ffmpeg -f lavfi -i color=blue,trim=duration=0.04 \
	-f lavfi -i anullsrc,atrim=duration=2 \
	-movflags +empty_moov+hybrid_fragmented \
	-frag_duration 1000000 \
	-frag_interleave 1 \
	output.mp4

1. first_track is the first track with track->entry != 0. As in the
command above, video track (track index 0) has a single frame. When
flush the second fragment, first_track is 1, the audio track.

2. write_moof = i == first_track, so write_moof is false for i = 0.

3. When mov->frag_interleave != 0, mov->mdat_buf != NULL, because
it contains audio data. So avio_write is called before write_moof,
that is, the data write before moof, and mov_finish_fragment
executed with wrong mdat_start.

4. With normal fmp4 output, the error isn't obvious. With
hybrid_fragmented, ffplay output.mp4 shows a lot of error messages.

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>

2025-06-01 16:36:54 +08:00