I don't know if I ran into the same problem as mrarlen, exactly. I had the "track outbound clicks & downloads" option turned on in the Google Analytics for WordPress plugin. It was rewriting the embedded javascript for the (HTML5) audio player in such a way that the HTML was no longer syntactically correct. This caused the embedded player to not work. Turning off that option fixed my problem.
I think this is actually a bug in the Google Analytics for WordPress plugin, so I don't expect there's anything you can do about it, but maybe this note will alert other users to the problem.