[FFmpeg-trac] #10135(avformat:new): matroska/ass: Wrong AVPacket duration set for ass events with 0 duration

[FFmpeg]

#10135: matroska/ass: Wrong AVPacket duration set for ass events with 0 duration
----------------------------------+--------------------------------------
             Reporter:  enen92    |                     Type:  defect
               Status:  new       |                 Priority:  normal
            Component:  avformat  |                  Version:  git-master
             Keywords:  mkv, ass  |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
----------------------------------+--------------------------------------
 Summary of the bug:

 Reported to Kodi (https://github.com/xbmc/xbmc/issues/21625) but the root
 cause seems to be in libav. The subtitle AVPackets returned from the
 demuxer have a duration > 0 that seems to result from the pts value that
 the next subtitle is received.

 Those subtitle events have start and end times equal to 0 and should not
 be shown:

 {{{
 Dialogue: 0,0:00:00.00,0:00:00.00,DCMain,CONAN,0000,0000,0000,,[ed]
 Dialogue: 0,0:00:00.00,0:00:00.00,DCMain,KOGORO,0000,0000,0000,,[eyecatch]
 Dialogue: 0,0:00:00.00,0:00:00.00,DCMain,,0000,0000,0000,,Detective Conan
 Episode 1047 "The \NRed Sheep's Eerie Game (Part One)"
 Dialogue: 0,0:00:00.00,0:00:00.00,DCMain,CONAN,0000,0000,0000,,[op]
 }}}

 Initially matroskadec sets the start and duration times correctly (both 0)
 but at some point along the chain the duration is changed.

 How to reproduce:
 {{{
 % ffplay -vf subtitles=filename="ass_sample.mkv" ass_sample.mkv

 ffmpeg version master built on linux (although it happens on all
 platforms)

 }}}

 The entries "[ed]", "[eyecatch]", "Detective Conan Episode 1047 "The \NRed
 Sheep's Eerie Game (Part One)", "[op]" should not be shown. Opening the
 same file with mpv shows the correct behaviour (they don't rely on the
 duration from AVPacket)
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10135>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker