I got to thinking about this and considered doing some work along the lines of evaluating what actually happens to audio once Youtube gets their grubby mitts on it... and someone beat me to it...
http://forum.recordingreview.com/content/youtube-audio-reverse-engineering-18/ (http://forum.recordingreview.com/content/youtube-audio-reverse-engineering-18/)
Definitely worth reading through what is there at least...
Eric
KB7DQH