mp3j player function vs short code

I installed a plugin which allows me to add a custom file upload field to my post so that I can upload an mp3 file. I would like to add a PHP function to my theme to read the url of this custom file and then display an mp3 player in the single.php page.

What is the function to do this? Can you just feed it a url and call the PHP function?

Thanks!

p.s. essentially what I am looking for is something like:

mp3_player($the_url_of_the_custom_field)

which will output all the javascript and html

http://wordpress.org/extend/plugins/mp3-jplayer/