YouTube is running an experiment asking some users to disable their ad blockers or pay for a premium subscription, or they will not be allowed to watch videos.
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.
They also can’t force you to look and listen to the current ads. So the “clever tracking” doesn’t need to be better than the status quo. What it could avoid is completely skipping ads as if they are not there. The server could reject giving you further frames until the time the ad runs is over. If you suppressed the ad, you still had to sit it out. Which in turn means that it’s (almost) futile for the user to do that. If I have to wait 2 minutes to watch, I might as well leave the ad running.
They also can’t force you to look and listen to the current ads. So the “clever tracking” doesn’t need to be better than the status quo. What it could avoid is completely skipping ads as if they are not there. The server could reject giving you further frames until the time the ad runs is over. If you suppressed the ad, you still had to sit it out. Which in turn means that it’s (almost) futile for the user to do that. If I have to wait 2 minutes to watch, I might as well leave the ad running.