I want to run videos on a second screen, but occasionally I need to check on a document or webpage so I'd like to quickly ALT+TAB to bring up the browser window and have it sit on top of the video screen, then I can minimize the browser once I'm done and the video is still there playing. (I'm doing this right now in reply to your message).

Think of it as an animated/audio desktop background.

I've found a workaround for now using Enhancer for Youtube's pop-out player.