[FFmpeg-trac] #10848(undetermined:new): Crackling when concatenating audio introduced in commit d85c6aba

[FFmpeg]

#10848: Crackling when concatenating audio introduced in commit d85c6aba
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             Reporter:  jonnyburger  |                     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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 Summary of the bug:

 We found that when upgrading to FFmpeg 6.1, a regression in audio quality
 has occurred when concatenating PCM-16 audio chunks into AAC.

 After bisecting 2000 commits, we find that the behavior has changed in
 https://github.com/FFmpeg/FFmpeg/commit/d85c6aba0cf27db2a6c4dfa3452cfb9c248d1b4a.
 This commit seems to have changed the test fixtures as well, indicating
 that it makes inadverted changes to the output.

 As of writing, the crackling is still on master.

 Important detail: The crackling is only audible on QuickTime on macOS with
 a relatively high volume. Playing the video for example in a browser does
 not result in audio artifacts.

 Repro: https://jonnyburger.s3.eu-central-1.amazonaws.com/crackling.zip
 Also uploaded as crackling.zip on the VideoLAN file uploader.

 To reproduce, you need to download the PCM chunks and concat them using:
 {{{
 ffmpeg -loglevel verbose -r 30 -f concat -safe 0 -i files.txt -c:v copy
 -c:a aac -b:a 320k output.mp4
 }}}

 Since the codebase has further evolved and it's not possible to just
 revert the commit, I derived a hacky fix for anyone else facing this issue
 (might break something else): https://jonnyburger.s3.eu-
 central-1.amazonaws.com/fix-aac.patch
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10848>
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