YouTube uses things like DASH, where they download pieces of the video from the server a bit at a time and feed into the browser's video pipeline. There's no s

YouTube uses things like DASH, where they download pieces of the video from the server a bit at a time and feed into the browser's video pipeline. There's no single link to the entire video, necessarily; you have to piece together the bits. This is one of the things that allows changing quality mid-video, btw. Furthermore, the video and audio are served separately so that codecs can be mixed and matched on the client side, and the same audio can be used for different quality video streams, etc. One of the things youtube-dl deals with is grabbing both and muxing into a single container. So yes, extracting things from YouTube is not trivial at all.