What Does YouTube Do To Your Video After You Upload It?

I don't think I've posted these two videos from Nat and Lo here before, but I was thinking about them recently because of YouTube's latest redesign. So much processing going on behind the scenes at a rate that is constantly adjusting to our changing internet connection speeds. All of this while making sure that there is no such thing as buffering -- just lower video quality which in a weird way, is preferred (at least for me).