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.
In theory they could do something funky, like: serve the first 20 seconds (an ad), then stall the connection until 20 seconds have passed, then serve the rest of the video. So you could seek around, but only after the ad was over. Not saying this is easy or feasible at scale, just that it is technically possible.
They’d have to disable allowing users to scrobble (move the time around) altogether.
In theory they could do something funky, like: serve the first 20 seconds (an ad), then stall the connection until 20 seconds have passed, then serve the rest of the video. So you could seek around, but only after the ad was over. Not saying this is easy or feasible at scale, just that it is technically possible.