I used to stream movies from my desktop over the local network with VLC and the main issue I faced was that I could never get the subtitles to work. I took a quick look at this repository and it doesn't look like they support subtitles either.
Perhaps they can be converted and shown using the WebVTT API[2] or <track> tags [3]?
Edit: Maybe that wouldn't work, here's a relevant stackoverflow post [4]
[1] https://en.wikipedia.org/wiki/SubRip
[2] https://developer.mozilla.org/en-US/docs/Web/API/WebVTT_API
[3] https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...
[4] https://stackoverflow.com/questions/61446205/webrtc-and-text...