There is an example of integrating Three.js and YouTube videos at
http://threejs.org/examples/css3d_youtube.html#cats
and examples of including general HTML elements (using CSS3D) at
http://learningthreejs.com/blog/2013/04/30/closing-the-gap-between-html-and-webgl/
and http://stemkoski.github.io/Three.js/CSS3D.html
Hope this helps!