[FFmpeg-trac] #8909(undetermined:new): Copying an AV1 stream from an MKV container to an MP4 container changes the reported framerate

FFmpeg trac at avcodec.org
Thu Sep 24 19:31:00 EEST 2020


#8909: Copying an AV1 stream from an MKV container to an MP4 container changes the
reported framerate
-------------------------------------+-------------------------------------
             Reporter:  veikk0       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:  AV1 MKV MP4  |               Blocked By:
  Matroska fps                       |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug: Copying some AV1 streams from an MKV container to an
 MP4 container changes the reported framerate and changes it from CFR to
 VFR.

 How to reproduce:
 Download the Sintel trailer, encode 10 seconds of it in AV1, print fps
 with ffprobe:
 {{{
 wget https://download.blender.org/durian/trailer/sintel_trailer-480p.mp4
 && ffmpeg -i sintel_trailer-480p.mp4 -an -c:v libsvtav1 -t 10 -preset 8
 sintel.mkv && ffprobe -v error -select_streams v:0 -show_entries
 stream=avg_frame_rate -of default=noprint_wrappers=1:nokey=1 sintel.mkv
 }}}
 Frame rate is the same as the source (24/1).

 Now to copy the freshly encoded video stream from the Matroska container
 to an MP4 container, and check out the frame rate:
 {{{
 ffmpeg -i sintel.mkv -c:v copy sintel.mp4 && ffprobe -v error
 -select_streams v:0 -show_entries stream=avg_frame_rate -of
 default=noprint_wrappers=1:nokey=1 sintel.mp4
 }}}
 It has changed to 80000/3333. Furthermore, the mediainfo program will now
 report that the file is variable frame rate instead of constant (not sure
 how to check this with ffprobe).

 Version info:
 {{{
 ffmpeg version N-99352-gd8ce8e8
 built with gcc 8 (Ubuntu 8.4.0-1ubuntu1~18.04)
 }}}

 If your FFmpeg isn't built with SVT-AV1 or libaom, I was also able to
 reproduce the issue by copying an existing AV1 file not authored with
 FFmpeg (as far as I know):
 http://download.opencontent.netflix.com.s3.amazonaws.com/AV1/Chimera/Old
 /Chimera-AV1-8bit-1920x1080-6736kbps.mp4. Copy video stream to an MKV,
 then copy that stream to an MP4. Same issue.

 The issue doesn't seem to crop up when going from other containers to an
 MP4, or when encoding directly to an MP4. Seems like this is specific to
 Matroska.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/8909>
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