According to the docs of jPlayer http://www.jplayer.org/latest/developer-guide/#jPlayer-essential-formats, you are only supposed to use either mp3 or m4a.  But in my case, I’m not sure which gets passed to the player from the database. So, I had to handle that in the script. Here’s what it looks like:

$("#jplayer").jPlayer({  
 ready: function() {
 $("#jp_container .track-default").click();
 },

 supplied: "m4a, mp3, mv4"
 });

When I wire up the handlers, I check the file extension before passing the URL to the setMedia method, like this:

$(".play").click(function(e) {  
 var filename = $(this).attr("href");
 var ext = filename.split('.').pop();
Technorati Tags:
  
 if (ext == "m4a") {
 $("#jplayer").jPlayer("setMedia", {
 m4a: $(this).attr("href")
 });
 }
 else {
 $("#jplayer").jPlayer("setMedia", {
 mp3: $(this).attr("href")
 });

 }
  

A little hacky, but it works!