Unable to add .wav file to lightroom

Hi, 

I'm trying to add an audio file to a picture (like in Slideshow); example is dog's bark over a picture of that particular dog.  I can add while in Slidshow but then it says the music file is not well formed.  Now that I look at it do I need to change the file back to a .wav file?  Not sure how/why Apple decided to do that.  Thank you for your help!