[FFmpeg-trac] #6176(undetermined:new): Use of non-standard value (4) for displayUnit in webm containers

[FFmpeg]

#6176: Use of non-standard value (4) for displayUnit in webm containers
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             Reporter:  theo         |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  3.2.1
  undetermined                       |               Blocked By:
             Keywords:  webm,        |  Reproduced by developer:  0
  matroska, aspect ratio             |
             Blocking:               |
Analyzed by developer:  0            |
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 Hi,

 Starting ffmpeg 3.2.x we have noticed that for Webm containers, ffmpeg
 sometimes (quite often for us actually) sets the displayUnit field to a
 value of '4' (likely from here:
 https://github.com/FFmpeg/FFmpeg/blob/e7dec52d4da7fad61f65529d5a396968e3dfe777/libavformat/matroskaenc.c#L1245
 ). I believe that according to the Webm documentation
 https://www.webmproject.org/docs/container/#DisplayUnit '4' is not a valid
 value for Webm containers.

 You can find link to a file to repro on this Shaka-packager thread:
 https://github.com/google/shaka-packager/issues/192 as well as previous
 discussion related to this.


 How to reproduce:
 ffmpeg version 3.2+

 ffmpeg -i original.mp4 -c:v libvpx-vp9 -pass 1 -b:v 0 -crf 33 -r 30
 -threads 8 -speed 4 -tile-columns 6 -frame-parallel 1 -g 60 -an -f webm -y
 /dev/null
 ffmpeg -i original.mp4 -c:v libvpx-vp9 -pass 2 -b:v 0 -crf 33 -r 30
 -threads 8 -speed 4 -tile-columns 6 -frame-parallel 1 -g 60 -auto-alt-ref
 1 -lag-in-frames 25 -c:a libvorbis -b:a 64k -f webm -y input.webm

 Original file https://www.dropbox.com/s/4hhx3o1hs89f5q3/input.webm?dl=0

 Thanks!

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Ticket URL: <https://trac.ffmpeg.org/ticket/6176>
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