[FFmpeg-trac] #8924(undetermined:new): Concat demuxer shifts video stream start time

[FFmpeg]

#8924: Concat demuxer shifts video stream start time
-------------------------------------+-------------------------------------
             Reporter:  cake_donkey  |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:  concat       |               Blocked By:
  demuxer start_pts start_time       |
  shift                              |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:

 After processing an mp4 file with the concat demuxer and using `-c copy`
 flag, the start_pts and start_time of the output file becomes shifted.
 This causes the output file to initially display a blank frame when it is
 first opened.

 Ffmpeg version used:
 {{{
 ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
 built with Apple clang version 11.0.3 (clang-1103.0.32.62)
 configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1 --enable-shared
 --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-
 cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl
 --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame
 --enable-libopus --enable-librav1e --enable-librubberband --enable-
 libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora
 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp
 --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid
 --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r
 --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb
 --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr
 --enable-videotoolbox --disable-libjack --disable-indev=jack
 libavutil      56. 51.100 / 56. 51.100
 libavcodec     58. 91.100 / 58. 91.100
 libavformat    58. 45.100 / 58. 45.100
 libavdevice    58. 10.100 / 58. 10.100
 libavfilter     7. 85.100 /  7. 85.100
 libavresample   4.  0.  0 /  4.  0.  0
 libswscale      5.  7.100 /  5.  7.100
 libswresample   3.  7.100 /  3.  7.100
 libpostproc    55.  7.100 / 55.  7.100
 }}}

 How to reproduce:

 Given an mp4 file containing video and audio stream `before.mp4`

 Run command `ffprobe before.mp4 -show_streams`, observe that video stream
 `start_time` and `start_pts` are 0.

 Given a txt file `concat.txt` with content:
 {{{
 file before.mp4
 }}}

 Run command `ffmpeg -f concat -i concat.txt concat.mp4`

 Run command `ffprobe concat.mp4 -show_streams`, observe that video stream
 `start_pts` and `start_time` are now non-zero.

 Patches should be submitted to the ffmpeg-devel mailing list and not this
 bug tracker.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/8924>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker