I also work on player stuff with OP and learned a lot in this process.
I did manage to get Air NZ to caption videos too, but not sure if they still do. Their marketing person changed years back and they didn't bother continuing with it (for a time anyway - with uBlock and such, I don't see any marketing from them anymore), even though the metrics that came back from the captioning experiment were incredible.
Then I got on an international flight and the safety video had captions for every language... except English. Ha.
If only a senior dev could get a job in which a11y is a priority. It is something I wish to specialise in more so.
I've found with NZ companies nobody seems to care (because there's bugger all legislation in NZ for this).
The funny thing is I'm someone who finds it difficult to hear people in noisy environments. But I never seem to have a problem with films or TV. Even films that many people seem to have trouble with, like Tenet.
My girlfriend always wants them on, though. I don't get it. But I have at least a couple of theories about why this is.
Firstly, she's a way faster reader than me. She reads easily twice as fast as me. But reading always takes priority in my brain. I can't not read a caption if it's on screen and that increased mental burden reduces my enjoyment.
Secondly, we watch things in different ways. When I watch something, it has 100% of my attention. Anything else is background noise, which I don't like. I'm much more selective about what I watch for that reason, as it's a bigger commitment. That means my listening circuits are fully engaged, but also I'm fully immersed in the film which means I benefit from additional context which is super important for listening.
All this to say, I turned on subtitles within one episode and it made for a much better viewing experience. Once I was able to read along I had no issue at all understanding the words too, but without the cue it was impossible.
Older media seems to have a more even mix. It is probably a 5.1 through my stereo speakers thing but I'm not sure how to fix it or if even can be fixed.
On anime and children's shows, the theme songs were frequently subtitled. I assumed this was so viewers could appreciate the lyrics
Comedy, skit and variety shows, where the dialog and commentary is mostly banter amongst a cast of "wacky" hosts. Here, subtitles (almost always in a garish, colorful font) served to punctuate jokes or funny lines, in the same way that a laugh track on an American sitcom is used to let the audience know when to laugh (even though the Japanese shows usually had a laughing studio audience as well).
Some shows did (do?) go overboard with the "comedic" subtitles, to a point where they were subtitling almost every other line a host said.
So, it's just like conversations in any language: basic, rambling, and emotive.
I do wish closed captioning worked better with speed controls, though.
For local playback of media files, I use daum kakao Potplayer, I have never come across something more power user friendly. MPV is weaker in a lot of areas, in my opinion. Potplayer interfaces with everything I'd want including vaporsynth and madvr and it has options for subtitle resync based on a multiplier and also converting based on framerate 60 -> 30. There is even an option for live subtitle translations. I personally like using it with smooth video project, but I understand it's not everyone's taste.
I really enjoyed having the captions for so many other reasons that I never turned them off. It’s great for multi-tasking and avoiding interruptions from environmental sounds like barking dogs, loud annoying children, phone calls, et cetera.
I enable captions sometimes for single words, which I failed to hear right, although usually in those instances captions show something completely nonsensical.