.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.

AVAssetWriter *assetWriter = [[AVAssetWriter assetWriterWithURL:exportURL

                                                       fileType:AVFileTypeWAVE

                                                          error:&assetError]







NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:

                                [NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey, 

                                [NSNumber numberWithFloat:41000.0], AVSampleRateKey,

                                [NSNumber numberWithInt:2], AVNumberOfChannelsKey,

                                [NSData dataWithBytes:&channelLayout length:sizeof(AudioChannelLayout)], AVChannelLayoutKey,



                                [NSNumber numberWithInt:16], AVLinearPCMBitDepthKey,

                                [NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,

                                [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,

                                [NSNumber numberWithBool:NO], AVLinearPCMIsBigEndianKey,

                                nil];

AVAssetWriterInput *assetWriterInput = [[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio

                                                                           outputSettings:outputSettings]

                                        retain];

Any help on compressing or using my AVAssetWritter to write to different codec instead of WAVE or CoreAudioFormat would be greatly appreciated.

EDIT: If there is a way to go straight from the music library to .m4a instead of .wav this would be the ideal approach I would like to take!

Thanks, Nick

ANSWER

This is the correct audio options for .m4a and if you want the user to see it as an .mp3 or .wav file just append those onto the end of the file name!

AudioChannelLayout channelLayout;

memset(&channelLayout, 0, sizeof(AudioChannelLayout));

channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;

NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:

                                [NSNumber numberWithInt: kAudioFormatMPEG4AAC], AVFormatIDKey,

                                [NSNumber numberWithFloat:44100.0], AVSampleRateKey,

                                [NSNumber numberWithInt:2], AVNumberOfChannelsKey,

                                [NSNumber numberWithInt:128000], AVEncoderBitRateKey,

                                [NSData dataWithBytes:&channelLayout length:sizeof(AudioChannelLayout)], AVChannelLayoutKey,                  



                                nil];