[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     |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:  ffmpeg
              Version:  unspecified  |               Resolution:
             Keywords:  ffmpeg       |               Blocked By:
  disposition metadata               |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Comment (by droid-xx):

 Initially when I created this ticket I thought that some dispositions
 (like "hearing_impaired") were kind of metadata switches that can be
 turned on/off for any type of stream inside any container. Part of the
 confusion arises from lack of documentation and the fact that ffprobe
 always returns ALL disposition types irrespective of stream or container,
 but it should probably only return the dispositions that are applicable to
 a particular stream type inside a particular container.

 Now I realize that the ability to set disposition types depends on the
 container (and maybe on the stream type?). As far as I can gather after
 further investigating about this by searching through ffmpeg-devel and
 trying to figure out the relevant parts of the source code, it seems that
 the dispositions "clean_effects", "hearing_impaired", "visual_impaired"
 (as an example) correspond to the audio_type field of the MPEG-2 ISO 639
 language descriptor.

 But I've tried setting these three flags to AC3 and mp2 audio streams
 inside different .ts containers, and all of them failed (disposition
 settings were ignored). So it seems this isn't just about Matroska,
 because I can't set any disposition other than Forced or Default in any
 container that I tried so far.

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Ticket URL: <https://trac.ffmpeg.org/ticket/9105#comment:3>
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