App crashing after selecting audio in iOS 7, fine on iOS 6 - ios7

Question

When selecting a song from the users library on either iPhone or iPad devices running iOS7 my app crashes out
The line it stops on is
FourCharCode formatID = audioDesc->mFormatID;
With a EXC_BAD_ACCESS code
Trying to check the console for more info, this is the last step it mentions;
appMake[8392:60b] Select music AssetUrl = (null)
Code below for the export session part;
- (void)exportAssetAsSourceFormat:(MPMediaItem *)item {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];
NSURL *assetURL = [item valueForProperty:MPMediaItemPropertyAssetURL];
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc]
initWithAsset:songAsset
presetName:AVAssetExportPresetPassthrough];
NSArray *tracks = [songAsset tracksWithMediaType:AVMediaTypeAudio];
AVAssetTrack *track = [tracks objectAtIndex:0];
id desc = [track.formatDescriptions objectAtIndex:0];
const AudioStreamBasicDescription *audioDesc = CMAudioFormatDescriptionGetStreamBasicDescription((CMAudioFormatDescriptionRef)desc);
FourCharCode formatID = audioDesc->mFormatID;
NSString *fileType = nil;
NSString *ex = nil;
switch (formatID) {
case kAudioFormatLinearPCM:
{
UInt32 flags = audioDesc->mFormatFlags;
if (flags & kAudioFormatFlagIsBigEndian) {
fileType = #"public.aiff-audio";
ex = #"aif";
} else {
fileType = #"com.microsoft.waveform-audio";
ex = #"wav";
}
}
break;
case kAudioFormatMPEGLayer3:
fileType = #"com.apple.quicktime-movie";
ex = #"mp3";
break;
case kAudioFormatMPEG4AAC:
fileType = #"com.apple.m4a-audio";
ex = #"m4a";
break;
case kAudioFormatAppleLossless:
fileType = #"com.apple.m4a-audio";
ex = #"m4a";
break;
default:
break;
}
exportSession.outputFileType = fileType;
NSString *exportPath = [[NSTemporaryDirectory() stringByAppendingPathComponent:[EXPORT_NAME stringByAppendingPathExtension:ex]] retain];
if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) {
[[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
}
exportSession.outputURL = [NSURL fileURLWithPath:exportPath];
[exportSession exportAsynchronouslyWithCompletionHandler:^{
if (exportSession.status == AVAssetExportSessionStatusCompleted) {
NSLog(#"export session completed");
//return YES;
[self performSelectorOnMainThread:#selector(gotoMainView:)
withObject:[EXPORT_NAME stringByAppendingPathExtension:ex]
waitUntilDone:NO];
} else {
NSLog(#"export session error");
//return NO;
}
[exportSession release];
}];
[pool release];
}
Media picker code;
- (void) mediaPicker: (MPMediaPickerController *) mediaPicker didPickMediaItems: (MPMediaItemCollection *) mediaItemCollection
{
// Dismiss the media item picker.
[self dismissModalViewControllerAnimated: YES];
if ([mediaItemCollection count] < 1) {
return;
}
[selectedItem release];
selectedItem = [[[mediaItemCollection items] objectAtIndex:0] retain];
NSURL* filePath = [selectedItem valueForProperty: MPMediaItemPropertyAssetURL];
NSLog(#"Select music AssetUrl = %#", filePath);
[viewLoading setHidden:NO];
[self UnloadSound];
[NSThread detachNewThreadSelector:#selector(exportAssetAsSourceFormat:) toTarget:self withObject:selectedItem];
}