[darau1]

Either awesome or i3 used to allow me to fullscreen a video, then pop that fullscreen video out into it's own floating window, that I could then stick on top of all other windows, and make it stay on every workspace. Really cool way to get a hacky picture in picture mode way before firefox did this.

[Fnoord]

VLC has a feature called "float on top". Together with resizing, it allows basically something akin to picture in picture mode. You can use VLC to play YouTube videos by downloading them with youtube-dl. That is what I used before Firefox PiP mode was available in stable.

[aasasd]

VLC can play YouTube directly―at least if YouTube didn't change the format again. Just ‘open’ the URL as a network source.

[anticensor]

They changed the playlist format. It has been failing again.

[tetris11]

Yep, but now you have a video window with a fixed window title, regardless of Tab, which makes it infinitely easier to programming window rules for.

[Jestar342]

Yep, sticky containers. Allows you to stick a container to an output, floating above all workspaces on that output.