As I already said in another thread several days ago, not quite. For most videos, yes, you do a request to https://www.youtube.com/get_video_info?video_id=... and there are links to files and adaptive streaming playlists. But then there's stuff like VEVO music videos, and those have an additional layer of protection in the form of some signature IIRC that you need to add to those stream URLs to make them valid.

Source: I added a custom YouTube player to my app several years ago, and, actually, besides my own reverse engineering, youdube-dl sources were quite helpful with figuring it all out. It didn't play those "protected" videos though.