http://youtube.googleapis.com/v/video url here?version=2&autoplay=1

remove http://youtu.be/UKSv0rxbduM

example http://youtube.googleapis.com/v/UKSv0rxbduM?version=2&autoplay=1

New 2015
http://www.youtube.com/v/Cn4R8Y-hRfY?autoplay=1