Well, you already got your HTML5 method, but you can also do it the Tenshi way with any YouTube video. You just get the embed link, change width and height to 1 (or put style="display:none" after "iframe"), and add "?autoplay=1" to the end of the src attribute. e.g.:
<iframe style="display:none" width="1" height="1" src="https://www.youtube.com/embed/aOvTF2gBBAE?autoplay=1" frameborder="0" allowfullscreen></iframe>
With both of these methods, the music does stop every time a new page is loaded, and neither works with mobile devices since they won't autoplay anything.