The clever check is impossible. The server can't know the client is showing the video even when playing DRM content. I could literally mute the sound and put a black box over the ad until it's over. The problem is as old as the internet itself.

That's why Apple and Meta pushing eye tracking so hard. It's the only solution to the ad blocking problem.

I think YT is doing well with YT premium and that's the way to go for them. It's one of my favorite subscriptions and I'd probably stick around even if they raise the price unless they hurt the creators so badly they bounce and I'd bounce with them.