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.
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| @@ -6509,9 +6509,9 @@ static int mov_flush_fragment(AVFormatContext *s, int force) · 6508 unmodified lines | |||
| 6509 | int buf_size, write_moof = 1, moof_tracks = -1; | 6509 | int buf_size, write_moof = 1, moof_tracks = -1; |
| 6510 | uint8_t *buf; | 6510 | uint8_t *buf; |
| 6511 | 6511 | ||
| 6512 | if (!track->entry) | ||
| 6513 | continue; | ||
| 6512 | if (mov->flags & FF_MOV_FLAG_SEPARATE_MOOF) { | 6514 | if (mov->flags & FF_MOV_FLAG_SEPARATE_MOOF) { |
| 6513 | if (!track->entry) | ||
| 6514 | continue; | ||
| 6515 | mdat_size = avio_tell(track->mdat_buf); | 6515 | mdat_size = avio_tell(track->mdat_buf); |
| 6516 | moof_tracks = i; | 6516 | moof_tracks = i; |
| 6517 | } else { | 6517 | } else { |