Dunno, I tried loading a YouTube page and capturing packets. Only ports in use were 443 and 80, even to the cdn-like hostnames (bla.c.youtube.com). First packet shows "GET /videoplayback?...."
A port number is just a port number, it doesn't define what protocol is in use. You can serve different protocols across it - the limitation is that generally you can only have one service listening on a port number. A youtube page will require a couple of different protocols.
It is not transported over HTTP, although it does make use of HTTP at the Application Layer. It is transported over TCP, which is a Transport Layer protocol.
HTTP has become a generic TCP wrapper for the common request->response pattern.