[FFmpeg-trac] #11602(undetermined:new): Muxing MKV and adding external SRT as anything except the only subtitle stream in an MKV prevents subtitle display in VLC

[FFmpeg]

#11602: Muxing MKV and adding external SRT as anything except the only subtitle
stream in an MKV prevents subtitle display in VLC
-------------------------------------+-------------------------------------
             Reporter:  Kurt         |                     Type:  defect
  Fitzner                            |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:  mkv srt      |               Blocked By:
  muxer remux                        |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 When re-muxing an MKV video that already has subtitle streams in it to add
 an additional external subrip .srt file, if the external .srt is included
 as anything except the only subtitle stream in the output then the added
 external subtitle will not display in VLC or on a Roku media player.

 You can select any number of existing subtitle stream from the input MKV
 video and they will properly copy to the output and display when the video
 is played.

 The following produces videos where the added external subtitle DOES NOT
 display, but where the subtitle stream included from the input .mkv DOES
 display:
 {{{
 % ffmpeg -report -i invid.mkv -i 1b.srt -map 0:v? -c:v copy -map 0:a? -c:a
 copy -map 0:s:0 -c:s:0 copy -map 1:s:0 -c:s:1 copy outvid1.mkv
 % ffmpeg -report -i invid.mkv -i 1b.srt -map 0:v? -c:v copy -map 0:a? -c:a
 copy -map 1:s:0 -c:s:0 copy -map 0:s:0 -c:s:1 copy outvid2.mkv
 }}}
 The following produces a video where the added external subtitle (the same
 one as the above) DOES display properly:
 {{{
 % ffmpeg -i invid.mkv -i 1b.srt -map 0:v? -c:v copy -map 0:a? -c:a copy
 -map 1:s:0 -c:s:0 copy outvid3.mkv
 }}}

 This was attempted on ffmpeg Windows 64 builds:
 ffmpeg version 2025-05-07-git-1b643e3f65-full_build-www.gyan.dev
 ffmpeg version 2025-05-19-git-c55d65ac0a-full_build-www.gyan.dev
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11602>
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