youtube-dl can fetch a video via its ID, the part after the "/watch?v=<ID>" in the URL. Combined with a video player, such as vlc, mpv, mpc-hc or similar, you can stream youtube videos without viewing from the youtube website. There are scripts available that make this less DIY, such as ones that launch your video player with youtube-dl when you load a page on youtube, though I do not have any of those on hand to show you.