[FFmpeg-trac] #7932(avformat:new): tee muxer: produces incorrect start_time, PTS

[FFmpeg]

#7932: tee muxer: produces incorrect start_time, PTS
-------------------------------------+-------------------------------------
             Reporter:  sbalko       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  avformat     |                  Version:  git-
             Keywords:  tee,         |  master
  start_time, pkt_pts_time           |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 The tee muxer changes the PTS times (and hence, the start_time). That is,
 when we transcode an input video (https://drive.google.com/file/d
 /1qM40ZzOa10HJY7vZt0b-bx191eYBqqM_/view?usp=sharing, "Big Buck Bunny" WebM
 trailer) directly into MP4 like so:

 ffmpeg -t 3 -i bunny.webm -vcodec libx264 -map 0:v bunny1.mp4

 ...we get an output video with a start_time property of 0.000000. In
 contrast, when using the "tee" muxer (for the sake of simplicity, with a
 single output only) like so:

 ffmpeg -t 3 -i bunny.webm -vcodec libx264 -map 0:v -f tee
 "[f=mp4]bunny2.mp4"

 ...we get an output video, where the start_time property is 0.080000. We
 confirmed that both videos have the same number of frames, where the
 pkt_pts_time properties of bunny2.mp4 are +0.08 sec shifted.

 How to reproduce:
 {{{
 ffmpeg version 3.4.6-0ubuntu0.18.04.1 Copyright (c) 2000-2019 the FFmpeg
 developers
 built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)
 }}}

 We can also reproduce this issue with a more recent FFmpeg build:
 {{{
 ffmpeg version N-93945-g02333fe394 Copyright (c) 2000-2019 the FFmpeg
 developers
 built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04)
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/7932>
FFmpeg <https://ffmpeg.org>
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