Incredible. But, one word: "screensaver".
(Especially, if anyone can do it, Chromecast screensaver!?)
1. Chrome > Dev tools > Network tab > Search "webm" (everybody uses html5 video, right?) > Right click a request, "copy as CURL".
2. Insert into CLI, remove &range=- parameter, and redirect output to some file (or use -o curl option)
3. mplayer somefile.webm -rootwin -vf scale=1920:1080 (or whatever)
I'm sure there's a better/easier way, but it's a start.