The content you want to reach is in an iframe on the page. BUT the problem is you will not be able to get to the content because the Same Origin Policy is going to prevent it.
document.getElementById("I0_1392927253257").contentWindow.document
SecurityError: Blocked a frame with origin "http://www.youtube.com" from accessing a cross-origin frame.
Check out @sashoalm's link below to change the context of iframe in Chrome.