If Youtube videos do not play reload the page, that's a Youtube bug.
Or maybe now, a few years later, it's a new bug ;-)

Zero 7 - Everything Up (Zizou) Joker & Ginz Remix

Noisia & Foreign Beggars - Shellshock

Laura Marling - Cross Your Fingers + Crawled Out Of The Sea

Laura Marling - New Romantic

Caribou - Hello Hammerheads (Tour Visuals)