[FFmpeg-trac] #8728(undetermined:open): Misplaced chapters for mp3 files (ID3v2 Chapter Frame Addendum)

[FFmpeg]

#8728: Misplaced chapters for mp3 files (ID3v2 Chapter Frame Addendum)
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             Reporter:  sandreas     |                    Owner:  (none)
                 Type:  defect       |                   Status:  open
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:
             Keywords:  chapters,    |               Blocked By:
  mp3, misplaced                     |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by sandreas):

 Replying to [comment:1 mkver]:
 > 1. Your file is gone; you should have uploaded it
 [https://streams.videolan.org/upload/ here] or attached it to this ticket
 in case of small samples.
 > 2. A quick test of mine shows that the chapters are offset by an amount
 corresponding to encoder delay. In fact, if one has an mp3 file with
 chapters and a xing frame indicating encoder delay, then each round of
 remuxing (without reencoding) offsets the chapters by this encoder delay.
 The demuxer just signals the encoder delay via side data and the
 AVStream's start_time. It is ffmpeg that offsets the chapters to
 (presumably) somehow compensate for this. This is definitely a bug
 (regardless of the missing sample).

 Thank yo for looking into this. The file is 33MB, so attachment did not
 work. The size is intended, with smaller files the issue is not fully
 reproducible. I uploaded the file to Videolan with reference project
 `ffmpeg` and gitlab ticket `#8728`, but it did not give me a reference to
 post here... As you already pointed out, it happens with the most mp3
 files that have chapters and should be easily reproducible using a merged
 version of https://librivox.org/history-of-a-six-weeks-tour-by-percy-
 bysshe-shelley/ (I used https://github.com/sandreas/m4b-tool/ with `m4b-
 tool merge audio_book_folder/ -o merged.mp3 --audio-channels 1 --audio-
 format mp3 --audio-bitrate 64k`, but it can also be done with raw ffmpeg,
 if you import the chapters correctly).
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/8728#comment:2>
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