[Feature] Display embedded subtitles

[cmcglownjr]

Is your feature request related to a problem? Please describe.
Currently mkv files that have subtitles embedded will not display those subtitles.

Describe the solution you'd like
Stash can display external captions but it should also be able to display embedded captions. Most desktop and mobile media players can display embedded captions so if possible can embedded captions be displayed in the Stash video player.

[7x5rg]

+1

[LewdCollector]

+1

[WithoutPants]

Videojs does not support displaying embedded subtitles.

There's a few possible ways that I can think of to display subtitles on the fly:

• have ffmpeg live transcode and embed the subtitles. This adds overhead that would be undesirable
• enable on-the-fly generation of subtitles. This is fast, but requires a bit of preparatory work before-hand and will need to be cached.

This improvement should be considered alongside the other caption bug-fixing/improvements (see #2619 and #3800).

In the meantime, this could probably be addressed with a plugin to generate srt files from files with embedded subs.

[WithoutPants]

$50 bounty assigned (contribution 745825)