HTML5 の Video Element で、以下の様にする事で複数のソースファイルを読み込みが可能。

<video controls="controls">
<source src="http://robertnyman.com/video/swedish-flag.mp4">
<source src="http://robertnyman.com/video/swedish-flag.ogv">
<p>Sorry, your web browser doesn't support the video element</p>
</video>

The video element in HTML5 – great possibilities, but also codec and licensing problems - Robert's talk
Video Demo