[FFmpeg-trac] #5058(undetermined:new): the concat filter does not respect the audio delay of the second segment

[FFmpeg]

#5058: the concat filter does not respect the audio delay of the second segment
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             Reporter:  redneb       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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 Suppose that you have two files, each having a video and an audio stream,
 and also that the second video's audio starts with a delay. If you try to
 concatenate them with the `concat` filter, then the resulting video will
 have sync problems with the audio portion that came from the second file.

 Here's a quick way to reproduce this:
 {{{
 ffmpeg -y \
         -filter_complex '
                 color=c=black:d=10[v1];
                 color=c=white:d=10[v2];
                 sine=d=10:f=220[a1];
                 sine=d=5,asetpts=PTS+5/TB[a2];
                 [v1][a1][v2][a2]concat=a=1
         ' \
         test.mkv
 }}}

 When I play the resulting file, the first 10 seconds are just like what I
 expected (black background with low pitched tone), but the remaining 10
 seconds are not. I was expecting that the higher pitched tone would start
 at 15s but it doesn't. Instead it starts at 10s. So basically, the
 `concat` filter simply concatenated the two audio streams without taking
 into consideration the 5 sec delay of the second one.

 I am not sure if this is a bug or the intended behavior, but I think it
 would be more reasonable if `concat` inserted silence at the beginning
 audio streams if necessary, just like it does with the end of such
 streams.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/5058>
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