Reimplement subtitle support

[chrisbenincasa]

Since we've removed the Plex transcoder, we need to bring back subtitle support with an 'in house' implementation. Of course, this is quite complicated, so we'll probably break it up into chunks:

1. Support for external subtitles first. These are simplest because we can just pull the file from Plex and feed it into the stream.
2. Support for extraction of embedded subtitles -- burning embedded subtitles into the output stream works well for local FS files (perhaps this can be an option with the 'direct' stream path), but when the stream input is coming from over the network, ffmpeg attempts to extract the subtitles out of the stream before playback starts, which is obviously a non-starter (it delays the stream)
3. Exposing these options and capabilities in the UI to some degree (e.g. "enable burn-in", background task configuration)

[ameturpoet]

I would love to see subtitles support in Tunarr - it makes it a lot harder to make anime channels without subtitles. Maybe an option for selecting a default audio track, too?

[cameronurnes]

Would love this, we pretty much always run with subtitles on my dizquetv setup

[avedor]

I don't really have much experience with typescript, but I'm happy to take a stab at getting external subs working!

[chrisbenincasa]

@avedor PRs always welcome!

[diblaze]

Would love subtitles to be implemented.
I am "semi" taking a look at it, just need to figure out if we already have information about existing subtitles already in StreamDetails that is being returned.

Or if we have to search for subtitles in the same folder as the file.
I am reusing the already existing LanguagePreferencesList, by appending subtitlePreferences where applicable.

[avedor]

I've taken a look a little at both embedded subs in an mkv container and at subs in the same dir. Jellyfin, at least, didn't seem to return the remote path for the subtitles or an ID, so may be more to implement than initially thought. I think I'm close on embedded subs, just can't seem to get ffmpeg to add the subtitles m3u8 to the master.m3u8 file, but this whole stack is new to me XD

I've been working on things in an MR on my fork that you're welcome to peep. Might help steer things along @diblaze

[avedor]

If i've understood things correctly, i've now mapped the subtitle stream the same way audio is mapped and the the only thing i have to figure out is how to get stream_vtt.m3u8 mapped into the master.m3u8 file so subtitles are actually associated with the media