[Fnoord]

Not sure about Plex and Kodi but Emby has a feature to automatically grab subtitles. It can search for the specific release (likely synchronised) or be more liberal with the added risk of getting a subtitle which doesn't sync. I think it uses Opensubtitles, and has no support for a different backend.

VLC uses Opensubtitles as well, but requires manual interaction. It can search for hash or name.

Both require an account (no API I think).

Subliminal you can run in a Docker environment (Emby as well, I suppose same with Plex and Kodi) to continuously grab subtitles for new releases.

Ideally, you want multiple providers for this. For example, Subscene and Addic7ed. AFAIK this isn't possible with any of the software I mentioned.

What I don't understand (actually, I think I do understand: it is because maintainers of subtitle platforms want to profit via ads) is why there's no incremental databases with subtitles (like we used to have with serials for software, forgot the name) so you can just select it offline. The amount of data is very little because its all text. With some compression and a database to search, it shouldn't cost a lot of resources. You can have a base, and then have incremental updates over that, with rebasing every once in a while. Kinda like HVSC (High Voltage Sid Collection).