How to change the source file of audio elements

Hi,

I am using adobe edge version 3 to add audio to a website.I use both .ogg and .mp3 files.

Inside the _edge.js file the audio element has 2 sources (one for .ogg and one for .mp3)

         {

                id: 'audio_element_id',

                type: 'audio',

                tag: 'audio',

                rect: ['0', '0','320px','45px','auto', 'auto'],

                source: ['source_file.mp3','source_file4.ogg']

         },

I want to change the source file of the audio_element programatically......

So i am using the following code inside edgeActions.js to change the source

sym.$("audio_element_id")[0].src="new_source_file.mp3";

But this will change the source of both(.mp3 and .ogg ) to  new_source_file.mp3

I want to change the source induvidually. What should i do??

Also I wanted to know what " [0] " stands for in " sym.$("my_audio_element")[0].play(); "

Please give me an example of a situation wherein i have to change the value of [0].

Thank you

Nithin