Its not too hard to detect ads in video streams, even old school analog VCR's could do that.
Watching TV shows without adds was one of the selling points of those back in the day.
Some more modern digital ones had near real time features where they would play with a delay of a lets say half an hour and used that time to remove the ads.
If you have stream from Youtube containing ads you can trivially skip ahead.
And Youtube could do nothing about it because random skipping is one of the base features of every video player ever.
Watching TV shows without adds was one of the selling points of those back in the day.
Some more modern digital ones had near real time features where they would play with a delay of a lets say half an hour and used that time to remove the ads.
If you have stream from Youtube containing ads you can trivially skip ahead.
And Youtube could do nothing about it because random skipping is one of the base features of every video player ever.