[FFmpeg-trac] #9086(undetermined:new): Cannot copy vp9 stream from webm to mp4

[FFmpeg]

#9086: Cannot copy vp9 stream from webm to mp4
-------------------------------------+-------------------------------------
             Reporter:  yrrqxk       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 I cannot copy the stream of this webm to an mp4 container. It can be
 copied to another webm and re-encoded to either webm or mp4 without issue.

 Copying this stream to another webm seems to also copy the defect as
 trying to copy from one webm to another then copy to mp4 results in the
 same error. This even happens with clips from affected files as you can
 see in the attached file.

 If this is relevant, the files are produced by youtube-dl and the issue
 only seems to happen when the video was in DASH format. This has been an
 issue for some time (months) across multiple youtube-dl versions and
 ffmpeg versions.
 How to reproduce:
 {{{
 ffmpeg.exe -i test.webm -c copy test.mp4

 ffmpeg version:
 2021-01-20-git-2021dbe1d6-full_build-www.gyan.dev

 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/9086>
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