[FFmpeg-trac] #7476(undetermined:new): Invalid pts and duration generated for mp4 when converting from webm

[FFmpeg]

#7476: Invalid pts and duration generated for mp4 when converting from webm
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             Reporter:  jyavenard    |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by Gyan):

 To be clear, I meant that ffmpeg will duplicate frames given the frame
 rate set for the output AVStream, if the muxing mode is CFR. not that the
 original WebM has duplicated frames. The vsync option lets you control
 that logic to some extent.

 CFR is default to MP4 but not all muxers, and is chosen because of a
 belief, not fully substantiated to me, that the MP4 muxer does not produce
 valid VFR files. It's too combersome, right now, to comb through all of
 ISO 14496-12/14 and identify what the requirements for VFR files are and
 how we fail to meet them.

 However, the primary issue here is the WebM demuxer and/or the conformity
 of the source video, not vsync or the MP4 muxer.

 For what it's worth, I see that neither your MP4 output nor mine shows
 video in Firefox 62.0.3/Win7 for me.

 I can get around that by setting an output rate.

     `ffmpeg -i MozilleTest -vsync vfr -r 40 -c:v libx264 test.mp4`

 This will drop frames whose duration < 1/40 s but not duplicate any
 frames.

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Ticket URL: <https://trac.ffmpeg.org/ticket/7476#comment:4>
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