The Red Bull Stratos Mission not only sets the record for the highest jump from a platform (128,100 feet) and maximum vertical velocity (Mach 1.24 = 833.9 mph), it also appears to be YouTube's most watched livestream to date.
This compares with approximately 500,00 concurrent livestreams (peak) during the London 2012 Olympic Games.
http://youtube-global.blogspot.com/