MPMediaItems raw song data

you can obtain the media item’s data in such way:

-(void)mediaItemToData
{
    // Implement in your project the media item picker

    MPMediaItem *curItem = musicPlayer.nowPlayingItem;

    NSURL *url = [curItem valueForProperty: MPMediaItemPropertyAssetURL];

    AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL: url options:nil];

    AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset: songAsset
                                       presetName: AVAssetExportPresetPassthrough];

    exporter.outputFileType = @"public.mpeg-4";

    NSString *exportFile = [[self myDocumentsDirectory] stringByAppendingPathComponent:           
                                                               @"exported.mp4"];

    NSURL *exportURL = [[NSURL fileURLWithPath:exportFile] retain];
    exporter.outputURL = exportURL; 

    // do the export
    // (completion handler block omitted) 
    [exporter exportAsynchronouslyWithCompletionHandler:
    ^{
    NSData *data = [NSData dataWithContentsOfFile: [[self myDocumentsDirectory] 
                                     stringByAppendingPathComponent: @"exported.mp4"]];

    // Do with data something

    }];
}

This code will work only on ios 4.0 and later

Good luck!