[FFmpeg-trac] #9646(undetermined:new): ffconcat issue slicing subtitle file

[FFmpeg]

#9646: ffconcat issue slicing subtitle file
-------------------------------------+-------------------------------------
             Reporter:  phyzical     |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 (this issue may contain a better summary than i can write up)
 (https://github.com/yt-dlp/yt-dlp/issues/2753)
 How to reproduce:
 {{{
 % ffmpeg -y -loglevel repeat+info -hide_banner -nostdin -f concat -safe 0
 -i 'file:CodysLab/processing/20220109.Cody'"'"'s Algae
 Panel.en.temp.srt.concat' -map 0 -dn -ignore_unknown -c copy -movflags
 +faststart 'file:CodysLab/processing/20220109.Cody'"'"'s Algae
 Panel.en.temp.srt'

 ffconcat version 1.0
 file 'file:processing/20220109.Cody'\''s Algae Panel.en.srt'
 inpoint 14.251000

 ffmpeg version 4.4.1 Copyright (c) 2000-2021 the FFmpeg developers
 built with gcc 10.3.1 (Alpine 10.3.1_git20211027) 20211027
 configuration: --prefix=/usr --enable-avresample --enable-avfilter
 --enable-gnutls --enable-gpl --enable-libass --enable-libmp3lame --enable-
 libvorbis --enable-libvpx --enable-libxvid --enable-libx264 --enable-
 libx265 --enable-libtheora --enable-libv4l2 --enable-libdav1d --enable-
 postproc --enable-pic --enable-pthreads --enable-shared --enable-libxcb
 --enable-libsrt --enable-libssh --enable-libvidstab --disable-stripping
 --disable-static --disable-librtmp --enable-libaom --enable-libopus
 --enable-libsoxr --enable-libwebp --enable-vaapi --enable-vdpau --enable-
 vulkan --disable-debug
 libavutil      56. 70.100 / 56. 70.100
 libavcodec     58.134.100 / 58.134.100
 libavformat    58. 76.100 / 58. 76.100
 libavdevice    58. 13.100 / 58. 13.100
 libavfilter     7.110.100 /  7.110.100
 libavresample   4.  0.  0 /  4.  0.  0
 libswscale      5.  9.100 /  5.  9.100
 libswresample   3.  9.100 /  3.  9.100
 libpostproc    55.  9.100 / 55.  9.100

 https://hub.docker.com/r/phyzical/yt-dlp/tags (docker container) running
 alpine (but has been confirmed without alpine)

 }}}

 "I am trying to concat subititles to remove sections to line up with media
 that has also been sliced"

 i did my best to summarise but the linked issue may do a better job of
 explaining the issue.

 "It cuts everything before ~14 seconds, but there is nothing in SRT before
 16 seconds, so FFmpeg throws an error. If I manually change 14 -> 17 in
 concat spec, FFmpeg succeeds.

 Expected behaviour in this case is to simply subtract 14.251 from all
 timestamps in SRT file."

 https://github.com/yt-dlp/yt-dlp/issues/2753
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9646>
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