As an end user, I never really saw much of Google Video's contributions. I'm sure they helped a lot in the backend, but the Youtube video player had all the core video features already when the two merged in my experience.
YouTube is 99.99% backend. The video player is peanuts to the infrastructure needed to process and serve the vomit-inducing amount of data. A quick search says 183 hours of video uploaded per minute and 694,000 hours of video watched per minute, served globally and rendered to dozens of resolutions and formats, and remember that unlike, say Netflix, this covers a much wider content library. (It's much easier to keep a few hundred gigs of data on global edge CDNs than god knows how many exabytes YouTube has.)
A lot of the stuff YT video provided was market related, Youtube initially had no licensing with media companies. So what eventually became content-ID wasn't acquired if I understand the history correctly, and I doubt YT could have been successful without that.
But yeah most of it was infrastructural it seems, both technologically and otherwise.
