[FFmpeg-trac] #9105(ffmpeg:new): Cannot set dispositions for subtitle streams inside MKV other than Default and Forced

[FFmpeg]

#9105: Cannot set dispositions for subtitle streams inside MKV other than Default
and Forced
-------------------------------------+-------------------------------------
             Reporter:  droid-xx     |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:
             Keywords:  ffmpeg       |  unspecified
  disposition metadata               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 I'm not sure whether this is a bug or a feature but I'm filing this since
 the documentation on disposition types is lacking details.

 If this is a feature, then there's probably some internal checking by
 ffmpeg to determine whether the disposition type given by the user can be
 applied to the selected stream. So obviously if you pass a disposition
 type of "attached_pic" to a subtitle it won't make any sense, hence
 nothing will change in the output disposition-wise (although there's no
 error or warning displayed to inform the user about this, and the
 documentation doesn't state which dispositions apply to which types of
 streams).

 However there are at least 2 more dispositions that can be set for
 subtitle streams: "karaoke" (for ass/ssa which are designed as karaoke
 subtitles) and "hearing_impaired" (for SDH subtitles).

 This works for the third subtitle track inside an .mkv with a total of 3
 subtitle streams:


 {{{
 ffmpeg -i input.mkv -map 0 -c copy -disposition:s:2 forced output.mkv
 }}}


 This won't work (disposition is ignored with no errors/warnings):


 {{{
 ffmpeg -i input.mkv -map 0 -c copy -disposition:s:2 hearing_impaired
 output.mkv
 }}}



 {{{
 ffmpeg -i input.mkv -map 0 -c copy -disposition:s:2 karaoke output.mkv
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/9105>
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