[FFmpeg-trac] #10551(ffmpeg:new): When copying chapters to an ogg file 1 second is added to the timestamp of some chapters

[FFmpeg]

#10551: When copying chapters to an ogg file 1 second is added to the timestamp of
some chapters
------------------------------------+----------------------------------
             Reporter:  giwiniswut  |                     Type:  defect
               Status:  new         |                 Priority:  normal
            Component:  ffmpeg      |                  Version:  6.0
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
------------------------------------+----------------------------------
 Summary of the bug:
 While converting a chaptered m4a (aac) audio to ogg (opus) I noticed that
 some chapters were off by one second, exactly. The decimal points are
 intact, the second timestamp has exactly 1s added onto it.
 While converting, ffmpeg prints the correct timestamps. When taking a look
 at the resulting file after conversion is done the timestamps are off.
 I do not see an obvious pattern as per which chapters are affected.

 Things work as expected if chapter information is manually converted to
 vorbiscomment chapter tags. (If that's what they're called, what I'm
 trying to refer to is this style of chapters in ffmetadata:)
 CHAPTER000=00:00:00.000
 CHAPTER000NAME=Chapter 1
 CHAPTER001=00:00:01.000
 CHAPTER001NAME=Chapter 2
 [...]
 FFmpeg & mpv properly pick up the chapters in this case.

 How to reproduce:
 {{{
 # Note: source.m4a is omitted, chapter information from ffmetadata.txt is
 attached instead.
 #       The issue is reproducible with that file alone.
 % ffmpeg -i source.m4a -map_metadata 0:s -f ffmetadata ffmetadata.txt
 % LENGTH='04:01:42.32'  # duration of source.m4a as reported in previous
 output
 % ffmpeg -f lavfi -i anullsrc -i ffmetadata.txt -map_chapters 1 -t
 "$LENGTH" ffmetadata.opus
 % ffmpeg -i ffmetadata.opus -map_metadata 0:s -f ffmetadata
 ffmetadata.opus.reexport.txt
 % diff ffmetadata.txt ffmetadata.opus.reexport.txt
 ==> Some chapters are off by 1s. The last END tag is adjusted to the
 precise length of the new file.

 # Note: resulting chapters.txt file is attached
 % echo ";FFMETADATA1" >chapters.txt
 % ffprobe -v error -of default=noprint_wrappers=1 -show_entries chapters
 source.m4a \
   | while read -r line; do
       tt="${line#TAG:title=}"
       if [ "$tt" = "$line" ]; then
           eval $line
       else
           stmp=$(date --date="@$start_time" --utc +'%T.%3N')
           printf 'CHAPTER%03d=%s\nCHAPTER%03dNAME=Chapter %d\n' $id
 "$stmp" $id $((id+1))
       fi
     done >>chapters.txt
 % ffmpeg -f lavfi -i anullsrc -i chapters.txt -map_metadata 1 -t "$LENGTH"
 chapters.opus
 % ffmpeg -i chapters.opus -map_metadata 0:s -f ffmetadata
 chapters.opus.reexport.txt
 % diff ffmetadata.txt chapters.opus.reexport.txt
 ==> All chapters are correct. Only the last END tag is adjusted to the
 precise length of the new file.


 ffmpeg version 2:6.0-9 as packaged by Arch Linux
 https://archlinux.org/packages/extra/x86_64/ffmpeg/
 built on 2023-09-05 17:55 UTC

 ffmpeg version git+release/6.0 at 3d5edb89e75fe3ab3a6757208ef121fa2b0f54c7
 commit date 2023-08-08 17:41:20 UTC
 }}}
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10551>
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