Not in OP's video. There's literally no way to escape the full-screen without pressing the escape key. You can't even double-click. I'm actually impressed by how user-hostile that video is.
> Why would I ever want to watch video not fullscreen?
Because the way they are doing it there is no minimize button. A less technically inclined person may not know that they have to press Escape (and now, it seems, some laptops have no hardware Esc button at all). In addition, the first time I played it, for some reason, Esc did not work and I had to Alt-Tab in order to leave the video.
I didn't check what this looks like on mobile, but I do the majority of my browsing on an iPad and while I use a physical keyboard with it, it doesn't have an escape button.
Presumably, this would use the usual mobile video player though, which does have a minimise button, so its likely not a real issue (I'm not on iPad right now so didn't check).
Because you're doing other stuff while listening to the audio.
>Youtube, which often totally hides the fullscreen button.
It's in the bottom right.