.wav to any compressed form from AVAssetWritter ios

Well the problem I am facing right now is a size issue problem. I am allowing the user to to choose a song from their library and then chop it up into pieces and then be able to use the .wav or .mp3 file on their computer with file sharing enabled. Basically I am using the following AVAssetWritter options and I keep getting a giant huge audio file. E.G. 5 minutes of music is about 50MB. I am looking to try and cut that down to an industry given standard size. I have a feeling it has to do with the fact I am using LinearPCM as one of my options but when I change that or any of the Audio Options the writer can not write. I am also changing the FileType parameter on the AVAssetWritter. Here is my code which works completely fine I just need to find away to compress or shrink the files.