[FFmpeg-trac] #7977(undetermined:new): First frame of VFR coming out short

[FFmpeg]

#7977: First frame of VFR coming out short
-------------------------------------+-------------------------------------
             Reporter:               |                     Type:  defect
  electron.rotoscope                 |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:  vsync        |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 When transcoding a variable framerate file using {{{-vsync cfr}}} and with
 a filtergraph, the first frame comes out a frame shorter than expected,
 which offsets the rest of the file. This doesn't happen when I don't have
 filters on, but I tried with setdar and drawtext so it doesn't seem to
 matter what filter is actually active.

 Comparing builds from https://ffmpeg.zeranoe.com/builds/win64/static/ this
 happens with the 20190329-9dece05 build and up to the current, but not on
 the 20190328-f8fa8bb build and previous.

 How to reproduce:
 {{{
 C:\current\bin\ffmpeg-20190328-f8fa8bb.exe -i "C:\current\testclip.mp4"
 -vsync cfr -filter_complex "[0:v]
 drawtext=:fontcolor=white:fontsize=18:text=\'\%%\{pts\}\'[vid]" -map
 "[vid]" "C:\current\out-20190328-f8fa8bb.mov"
 C:\current\bin\ffmpeg-20190329-9dece05.exe -i "C:\current\testclip.mp4"
 -vsync cfr "C:\current\out-20190329-9dece05-nofilter.mov"
 C:\current\bin\ffmpeg-20190329-9dece05.exe -i "C:\current\testclip.mp4"
 -vsync cfr -filter_complex "[0:v]
 drawtext=:fontcolor=white:fontsize=18:text=\'\%%\{pts\}\'[vid]" -map
 "[vid]" "C:\current\out-20190329-9dece05-ptstext.mov"
 C:\current\bin\ffmpeg-20190329-9dece05.exe -i "C:\current\testclip.mp4"
 -vsync cfr -filter_complex "[0:v]setdar=4/3[vid]" -map "[vid]"
 "C:\current\out-20190329-9dece05-setdar.mov"
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/7977>
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