[FFmpeg-trac] #8366(avformat:new): Audio ticks and video/audio out-of-sync when using MXF files with pre-charge

FFmpeg trac at avcodec.org
Tue Nov 19 12:51:29 EET 2019

#8366: Audio ticks and video/audio out-of-sync when using MXF files with pre-
             Reporter:  HenkDemper  |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avformat
              Version:  git-master  |               Resolution:
             Keywords:  MXF         |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |

Comment (by ngaullie):

 I have analyzed your files and I have another reading :
 - every picture sample is encoded to your MOV file, and every audio sample
 is rewrapped, there is no loss
 - the loss of sync (ffmpeg bug) does not seem to be related to the MXF
 wrapper itself. At the output, the MOV file has a video track with an edit
 list that shift video of 0.0667s (precisely=2/29.97) - but not the audio
 track, and this breaks sync.

 It you disables B-frames when encoding (-bf 0), there is no precharge
 signalization in the output, that should fix you problem, can you confirm


 The input MXF file has a precharge value which is consistent amongst the
 tracks (video/audios/tc), and I agree that, in this case, you can claim
 its's Op1a because this is the state of the art, broadly implemented,
 despite absence of clarification in actual texts.
 Support for MXF having non-consistent precharges values does not seem
 necessary in my opinion.
 Handling MXF files having a consistent precharge value like yours is no
 big deal with a first pass analysis and a basic trim clip switch; but of
 course this is not ideal and could be enhanced.

Ticket URL: <https://trac.ffmpeg.org/ticket/8366#comment:9>
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