Embed videos to autoplay in HD

This is what Google is using to automatically embed YouTube videos as HD playing.  Found this on their page featuring and announcing the new Google Maps.  This is how they displayed their promotional video *(using this code);

"https://www.youtube.com/embed/THxJHcR1D2c?enablejsapi=1&version=3&playerapiid=player&controls=1&autohide=1&rel=0&showinfo=0&vq=hd720"

So, to break that down a little bit: 

embed code looks like this:

?enablejsap=1&

playerapiid=player&

controls=1amp;

autohide=1&

rel=0&

showinfo=0&

vq=hd720

Pretty sure it's the last line that makes it possible.