Why does my html widget not play sound in ibooks?

I've designed a widget that plays sound correctly in every other browser. It uses an AAC-MPEG4 with the .m4a file extension on all of the sounds. I know the code is working correctly because as I said, it works in any browser. I've checked to volume controls and speakers of the ipad, they work and are turned all the way up. I just wonder if ibooks somehow does not support the javascript .play() command...