I remember learning somewhere (perhaps a Podcasts discussion?) that Bluetooth headphones can tell the host device what their audio delay is. Given that information to host device can adjust video playback so that the sound syncs up perfectly. I know iOS is capable of this, I'd assume macOS is well.

So it depends on the headphones.

Of course that only helps with premade content. If you're playing a game the OS can't adjust the game for 200 ms of lag, everything is just going to be out of sync.

I've always wondered how that worked! When watching a movie on my Linux laptop, it automagically syncs, even with a very poor quality promotional BT speaker that says "this bud's for you!" every time it pairs.

I've tried 4 different headphones from 3 different vendors with 2 different smart watches (Moto 360 Sport, now Polar M600). I've had the same problem with all of them.

At least one of the headphones has been a very high quality LG (HBS900?). Oddly, I've had the best connectivity with a cheapo freebie headphone set that has audio so bad that I can't stand to use them..