cyber, а если так:
var source = document.createElement('source'),
video = document.createElement('video');
source.type = 'video/mp4; codecs="avc1.42E01E, mp4a.40.2"';
source.src = 'http://cyberua.16mb.com/player/data/video3.mp4';
video.appendChild(source);
document.body.appendChild(source);