[mimimi31]

That wouldn't work for dynamically injected ads that could be at different timestamps and have different lengths for each user.

[meithecatte]

Some sort of checksumming to detect segments differing between users would probably be doable.

[_ache_]

I think you under estimated the cost of your solution, the cost must not excess the profit from the ad.

You need hard work on the encoder to do that (at least to segment video, because re-encoding dynamically is obviously not an option). Not profitable for Google.

[amelius]

Aren't there codecs that don't carry state across keyframes? Wouldn't it then be trivial to split a video at a keyframe and insert new content?

[15155]

Shazam-style audio fingerprinting can help.