Did you know that with CSS3 transforms, you can basically do 3D without using WebGL, or even canvas?
Well, the elements you define in html are still flat, but they are immersed in a projective space and you can apply any linear tranformation to them, including those you'd normally use with WebGL.
It could include any kind of HTML elements, even an iframe playing a video:
Give it a try : click and move your mouse (not inside the video though, but anywhere else in the body of the document).