Video⁄audio desync between segments in MPV and in VLC is delay between segments and missing subtitles

[456325]

Summary of the bug:
When i cut into 2 segments an .mp4 file that contains also subtitles and then merge the segments, it cause issue:
MPV player: desynchronization between segments
VLC player: delay between segments and missing subtitles

When i exclude subtitles, it plays without problem.

How to reproduce:

# put source.mp4 ( ​download-here ) into some directory (in my case /dev/shm/) and go to that directory inside a Linux terminal:

cd /dev/shm/

ffmpeg -hide_banner -ss '22.10829' -i 'source.mp4' -t '3.25325' -avoid_negative_ts make_zero -map '0:0' '-c:0' copy -map '0:1' '-c:1' copy -map '0:2' '-c:2' copy -map_metadata 0 -default_mode infer_no_subs -ignore_unknown -f mp4 -y 'source-seg2.mp4.mp4'

ffmpeg -hide_banner -ss '11.13900' -i 'source.mp4' -t '1.00100' -avoid_negative_ts make_zero -map '0:0' '-c:0' copy -map '0:1' '-c:1' copy -map '0:2' '-c:2' copy -map_metadata 0 -default_mode infer_no_subs -ignore_unknown -f mp4 -y 'source-seg1.mp4.mp4'

echo -e "file 'file:source-seg1.mp4.mp4'\nfile 'file:source-seg2.mp4.mp4'" | ffmpeg -hide_banner -f concat -safe 0 -protocol_whitelist 'file,pipe,fd' -i - -map '0:0' '-c:0' copy '-disposition:0' default -map '0:1' '-c:1' copy '-disposition:1' default -map '0:2' '-c:2' copy '-disposition:2' default -default_mode infer_no_subs -ignore_unknown -f mp4 -y 'destination-merged.mp4'

# Play to see described issue:
vlc destination-merged.mp4
mpv destination-merged.mp4

# When excluding subtitles, it plays without apparent problem:

ffmpeg -hide_banner -ss '22.10829' -i 'source.mp4' -t '3.25325' -avoid_negative_ts make_zero -map '0:0' '-c:0' copy -map '0:1' '-c:1' copy -map_metadata 0 -default_mode infer_no_subs -ignore_unknown -f mp4 -y 'source-seg2-nosubs.mp4.mp4'

ffmpeg -hide_banner -ss '11.13900' -i 'source.mp4' -t '1.00100' -avoid_negative_ts make_zero -map '0:0' '-c:0' copy -map '0:1' '-c:1' copy -map_metadata 0 -default_mode infer_no_subs -ignore_unknown -f mp4 -y 'source-seg1-nosubs.mp4.mp4'

echo -e "file 'file:source-seg1-nosubs.mp4.mp4'\nfile 'file:source-seg2-nosubs.mp4.mp4'" | ffmpeg -hide_banner -f concat -safe 0 -protocol_whitelist 'file,pipe,fd' -i - -map '0:0' '-c:0' copy '-disposition:0' default -map '0:1' '-c:1' copy '-disposition:1' default -default_mode infer_no_subs -ignore_unknown -f mp4 -y 'destination-merged-nosubs.mp4'

# Play to see no issue:
vlc destination-merged-nosubs.mp4
mpv destination-merged-nosubs.mp4