That’s a good question.
This lip sync issues are mostly present with the ATV4K device. On the main screen, use SDR4k 50hz, don’t use SDR 4k 23.97hz. when u use that, youtube audio video will be out of sync, if match frame rate is set to on .
I have this problem last time, with the old ATV. Enter the Xbox series X, everything locked down to 60hz and the problem went away.
However, Apple has this wireless audio sync feature to fix this problem
Go to audio settings and choose wireless audio sync, then use your iPhone, a pop up window will appear on your HP.
The ATV4K will play some test tones and your mobile phone will work as a microphone to calibrate the audio to sync to video. That’s it as above.
It should all work nicely.
Initially I thought it was the HD fury vertex 2 causing the delay, later I found out that latency is in the nano second range on the HD fury. So it’s nothing to do with that
Most often , If sound is ahead, then display is doing lot of processing, if video is ahead, then AVR is doing lot of processing.
In my case, sound was ahead, so it was display was either doing a lot of processing or mismatch frame rate issues. The problem at my place WS evident with YouTube content.Changing the settings from SDR 23.97hz to 50hz solved it