AVCaptureSession adding 2 inputs freezes preview layer - iphone

Question

If I just have the video added as an input, the preview layer works fine, and the video records fine, but if I try to add audio, the preview layer freezes, and video file is corrupted. What could be going on here that is causing all of this?
-(void) record {
AVCaptureSession *session = [[AVCaptureSession alloc] init];
[session beginConfiguration];
session.sessionPreset = AVCaptureSessionPresetMedium;
CALayer *viewLayer = self.vImagePreview.layer;
NSLog(#"viewLayer = %#", viewLayer);
AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
captureVideoPreviewLayer.frame = self.vImagePreview.bounds;
[self.vImagePreview.layer addSublayer:captureVideoPreviewLayer];
AVCaptureDevice *device = [self frontFacingCameraIfAvailable];
NSError *error = nil;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
if (!input) {
// Handle the error appropriately.
NSLog(#"ERROR: trying to open camera: %#", error);
}
AVCaptureDevice *audioCaptureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioCaptureDevice error:nil];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectoryPath = [paths objectAtIndex:0];
AVCaptureMovieFileOutput *movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
NSString *archives = [documentsDirectoryPath stringByAppendingPathComponent:#"archives"];
NSString *outputpathofmovie = [[archives stringByAppendingPathComponent:#"Test"] stringByAppendingString:#".mp4"];
NSURL *outputURL = [[NSURL alloc] initFileURLWithPath:outputpathofmovie];
[session addInput:input];
[session addInput:audioInput];
[session addOutput:movieFileOutput];
[session commitConfiguration];
[session startRunning];
[movieFileOutput startRecordingToOutputFileURL:outputURL recordingDelegate:self];
}
-(AVCaptureDevice *)frontFacingCameraIfAvailable
{
NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
AVCaptureDevice *captureDevice = nil;
for (AVCaptureDevice *device in videoDevices)
{
if (device.position == AVCaptureDevicePositionFront)
{
captureDevice = device;
break;
}
}
// couldn't find one on the front, so just get the default video device.
if ( ! captureDevice)
{
captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
}
return captureDevice;
}