Most viewers on YouTube do have sound on, making burned in captions not necessary. I’m not sure if they use the same system for closed captioning or not, but YouTube TV uses a different system as described above. YouTube accepts closed caption files (they use the term subtitle). That will obviously change as the system develops.

YouTube is playing around with AI for subtitles and it isn’t very good yet. AI can either perform captioning in advance or on the fly.

Once refined to a reliable standard, this will take over from the two manual methods as it will be cheaper, faster, and hopefully, more accurate than it is now. This technology is still in its infancy and often gets things wrong. Increasingly, studios are using AI to automatically generate subtitles and closed captions. These are then embedded into the broadcast, ready for use. Scripted shows will often create subtitles and closed captions in post-production using the script and interpretation of what happens on screen. This is then embedded into the broadcast to be picked up by your player. They listen to what’s going on and manually type the subtitles and sound cues into their stenograph machine. In some unscripted shows, like quiz shows or interviews where you don’t necessarily know what’s coming next, a human stenographer may create closed captions as the show unfolds.

Does youtube have closed caption