[FFmpeg-trac] #10379(ffmpeg:new): concat demuxer produces wrong duration for flac files

[FFmpeg]

#10379: concat demuxer produces wrong duration for flac files
-------------------------------------+-------------------------------------
             Reporter:               |                     Type:  defect
  slycordinator                      |
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:  git-
                                     |  master
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 Using the concat demuxer with flac files, the generated file's duration is
 that of the first file in the list
 How to reproduce:
 1) create two flac files
 In my case, I have one named half_sec.flac and another named 1_sec.flac.
 Both are silent files; half_sec is 0.5 seconds and 1_sec is 1.0 seconds in
 duration.
 2) concatenate them using the concat demuxer as explained at
 https://trac.ffmpeg.org/wiki/Concatenate#demuxer
 3) use ffprobe to see duration is equal to that of the first file and open
 in media player to see same
 {{{
 mylist.txt:
 file '/path/to/half_sec.flac'
 file '/path/to/1_sec.flac'

 % ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.flac
 ffmpeg version N-110692-gc4b3e882f8 Copyright (c) 2000-2023 the FFmpeg
 developers
   built with gcc 10 (Debian 10.2.1-6)
   configuration: --prefix=/usr/local --extra-libs='-lpthread -lm'
 --bindir=/usr/local/bin --disable-ffplay --disable-doc --disable-htmlpages
 --disable-manpages --disable-podpages --disable-txtpages --enable-libass
 --enable-libfdk-aac --enable-libaom --enable-libfreetype --enable-
 libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-
 libx264 --enable-libx265 --enable-gnutls --enable-static --enable-gpl
 --enable-nonfree
   libavutil      58.  9.100 / 58.  9.100
   libavcodec     60. 14.101 / 60. 14.101
   libavformat    60.  5.100 / 60.  5.100
   libavdevice    60.  2.100 / 60.  2.100
   libavfilter     9.  8.100 /  9.  8.100
   libswscale      7.  2.100 /  7.  2.100
   libswresample   4. 11.100 /  4. 11.100
   libpostproc    57.  2.100 / 57.  2.100
 Input #0, concat, from 'mylist.txt':
   Duration: N/A, start: 0.000000, bitrate: N/A
   Stream #0:0: Audio: flac, 44100 Hz, stereo, s16
 Output #0, flac, to 'output.flac':
   Metadata:
     encoder         : Lavf60.5.100
   Stream #0:0: Audio: flac, 44100 Hz, stereo, s16
 Stream mapping:
   Stream #0:0 -> #0:0 (copy)
 Press [q] to stop, [?] for help
 [out#0/flac @ 0x562a4f405d40] video:0kB audio:0kB subtitle:0kB other
 streams:0kB global headers:0kB muxing overhead: 3871.962617%
 size=       8kB time=00:00:01.44 bitrate=  47.2kbits/s speed=71.7x

 % ffprobe output.flac
 ...
 [flac @ 0x560349e5ed80] sample/frame number mismatch in adjacent frames
 Input #0, flac, from 'output.flac':
   Metadata:
     encoder         : Lavf60.5.100
   Duration: 00:00:00.50, start: 0.000000, bitrate: 136 kb/s
   Stream #0:0: Audio: flac, 44100 Hz, stereo, s16
 }}}

 Results:
 Duration of file is equal to the first file found in the temporary text
 file
 As in above output, the first file is 0.5 seconds, the second is 1.0
 seconds, the concatenated output file shows a duration of 0.5 seconds, and
 the file is 0.5 seconds long when opened in media players/audio editing
 utilities

 Expected:
 The total duration be the the total for all of the combined files and when
 opened in an editor/media player, the duration also be that of the
 combination of all files.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10379>
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