[Plugin: NextGEN Gallery] NextGen Gallery background music

I cannot get the background music to play through the slideshow. I am using an MP3 file (http://goodasyourwordframes.com/wp-content/uploads/2011/01/06-Great-Ocean.mp3)

Is MP3 okay, or does it need to be wav?
Is there a size limitation?

The site is http://goodasyourwordframes.com/

Thank you,
Andrew