One for the webtechs and vintage audiophiles- While not technically Youtube, this little snippet spun off an ongoing project of mine can still serve the purpose of ambient audio :)
http://www.psychsoftware.org/portfolio/software/chiptuneJS/chiptuneJS.html
It will currently
ONLY work in Chrome (desktop or Android; haven't tried iOS) or maybe the nightly/beta Firefox releases. Safari claims to have AudioContext but takes the OscillatorNode's .start() function as a cue to silently fail out of the script and pretend I never asked it for anything.
The key thing to note here is that I am using all of zero audio files for theoretically unlimited audio duration, much in the same way ye olde consoles and my old chiptune.cpp libraries did. Just pure sweet waveforms provided by the browser ^_^