[FFmpeg-trac] #10211(avfilter:new): Concat filter with `-re` (realtime) inputs does not keep realtimeness

[FFmpeg]

#10211: Concat filter with `-re` (realtime) inputs does not keep realtimeness
-------------------------------------+-------------------------------------
             Reporter:  Brad Isbell  |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  avfilter     |                  Version:  git-
                                     |  master
             Keywords:  concat       |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 When you use the `concat` filter to create a sequence of media from
 inputs, and when those inputs need to be forced to run in realtime with
 the `-re` option, only the first input runs in realtime.  Subsequent
 inputs run faster.

 Presumably, the subsequent inputs' realtime keeper is looking at the
 overall timestamp, and assuming it needs to catch up.

 An easy way to test this is with a timer (`date` command, in my case), and
 a couple `lavfi` inputs:

 {{{
 date; ffmpeg -re -f lavfi -i "sine=frequency=1000:duration=30" -re -f
 lavfi -i "sine=frequency=500:duration=30" -filter_complex "[0:a][1:a]
 concat=n=2:v=0:a=1" -f null NUL; date
 }}}

 {{{
 Tuesday, February 21, 2023 1:48:17 PM
 }}}

 {{{
 ffmpeg version 2023-02-19-git-2aec86695a-full_build-www.gyan.dev Copyright
 (c) 2000-2023 the FFmpeg developers
   built with gcc 12.2.0 (Rev10, Built by MSYS2 project)
   configuration: --enable-gpl --enable-version3 --enable-static --disable-
 w32threads --disable-autodetect --enable-fontconfig --enable-iconv
 --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma
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 --enable-libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-
 libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex
 --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite
 --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-
 chromaprint
   libavutil      58.  3.100 / 58.  3.100
   libavcodec     60.  4.100 / 60.  4.100
   libavformat    60.  4.100 / 60.  4.100
   libavdevice    60.  2.100 / 60.  2.100
   libavfilter     9.  4.100 /  9.  4.100
   libswscale      7.  2.100 /  7.  2.100
   libswresample   4. 11.100 /  4. 11.100
   libpostproc    57.  2.100 / 57.  2.100
 Input #0, lavfi, from 'sine=frequency=1000:duration=30':
   Duration: N/A, start: 0.000000, bitrate: 705 kb/s
   Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
 Input #1, lavfi, from 'sine=frequency=500:duration=30':
   Duration: N/A, start: 0.000000, bitrate: 705 kb/s
   Stream #1:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
 Stream mapping:
   Stream #0:0 (pcm_s16le) -> concat
   Stream #1:0 (pcm_s16le) -> concat
   concat:out:a0 -> Stream #0:0 (pcm_s16le)
 Press [q] to stop, [?] for help
 Output #0, null, to 'NUL':
   Metadata:
     encoder         : Lavf60.4.100
   Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
     Metadata:
       encoder         : Lavc60.4.100 pcm_s16le
 size=N/A time=00:00:59.97 bitrate=N/A speed=   2x     0x
 video:0kB audio:5168kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown
 }}}

 {{{
 Tuesday, February 21, 2023 1:48:47 PM
 }}}

 Note that both inputs were set to run realtime, and were of 30 seconds
 each, but the FFmpeg run finished in 30 seconds total.  Also note that the
 total audio output time was ~60 seconds, and that the speed was 2x.  Since
 it's supposed to run realtime, it should have taken 60 seconds and ran at
 1x.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10211>
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