[FFmpeg-trac] #7843(undetermined:new): FFmpeg not outputting to spec MKV files

[FFmpeg]

#7843: FFmpeg not outputting to spec MKV files
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             Reporter:               |                     Type:  defect
  alexrichmond                       |
               Status:  new          |                 Priority:  important
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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 Hello,

 It seems ffmpeg is not outputting valid mkv files according to MKValidator
 (0.5.2).

 MKValidator reports:
 ERR0B1: Block at 1020711 track #3 is not a keyframe
 over and over again.

 Please note these are errors & not warnings. If they were just warnings
 then I would just ignore the issue as warnings will still allow a file to
 be valid according to MKValidator.

 Track 3 is Subtitles. The subtitles are text copied from a satellite
 recording. The Subtitles are plain text, not pictures.

 Now, this gets more interesting, as If i run the mkv ffmpeg outputs
 through mkvtoolnix (just basic re-mux) and then test with MKValidator
 again, there are no issues at all; no warnings or errors.  So it looks
 like this is a issue with the way FFmpeg is dealing with subtitles in mkv
 containers.

 Here is my ffmpeg command line:
 ffmpeg -fix_sub_duration -txt_format text -i ./testrecording.ts -c:v
 libx264 -vf zscale=w=1280:h=720:f=spline36,setsar=1 -preset slow -crf 25
 -level 4.1 -c:a copy -c:s copy ./mysubstest.mkv

 Any ideas? Thanks for any help!

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Ticket URL: <https://trac.ffmpeg.org/ticket/7843>
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