AVCapture Session not found. Couldn't add video input - ios

Question

I'm trying to make a camera app using AVCaptureSession. For now I just want to see if the video input works or not. But it looks like there is no input and I can't seem to understand why.
- (void)viewDidLoad
{
[super viewDidLoad];
session = [[AVCaptureSession alloc] init];
[self addVideoPreviewLayer];
CGRect layerRect = [[[self view] layer] bounds];
[[self previewLayer] setBounds:layerRect];
[[self previewLayer] setPosition:CGPointMake(CGRectGetMidX(layerRect),
CGRectGetMidY(layerRect))];
[[[self view] layer] addSublayer:[self previewLayer]];
UIButton *myButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
myButton.frame = CGRectMake(80, 320, 200, 44);
[myButton setTitle:#"Click Me!" forState:UIControlStateNormal];
[myButton addTarget:self action:#selector(scanButtonPressed) forControlEvents:UIControlEventTouchDown];
[self.view addSubview:myButton];
}
-(void)addVideoPreviewLayer
{
[self setPreviewLayer:[[[AVCaptureVideoPreviewLayer alloc] initWithSession:[self session]] autorelease]];
[[self previewLayer] setVideoGravity:AVLayerVideoGravityResizeAspectFill];
}
-(void) addVideoInput
{
AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
if (videoDevice)
{
NSError *error;
AVCaptureDeviceInput *videoIn = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
if (!error)
{
if ([[self session] canAddInput:videoIn])
[[self session] addInput:videoIn];
else
NSLog(#"Couldn't add video input");
}
else
NSLog(#"Couldn't create video input");
}
else
NSLog(#"Couldn't create video capture device");
}
-(IBAction)scanButtonPressed
{
[self addVideoInput];
}

Answer 1

Here is how I do it. This is condensed from multiple functions, so it may not be compilable code, and error handling has been removed for the most part.
captureSession = [[AVCaptureSession alloc] init];
captureSession.sessionPreset = AVCaptureSessionPresetMedium;
AVCaptureDevice *videoDevice;
videoDevice = [self frontFacingCamera];
if (videoDevice == nil) {
videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
}
if ( videoDevice ) {
NSError *error;
videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
[captureSession addInput:self.videoInput];
}
videoOutput = [[AVCaptureVideoDataOutput alloc] init];
[videoOutput setAlwaysDiscardsLateVideoFrames:NO];
AVCaptureConnection *conn = [videoOutput connectionWithMediaType:AVMediaTypeVideo];
if (conn.supportsVideoMinFrameDuration)
conn.videoMinFrameDuration = CMTimeMake(1, frameRate);
if (conn.supportsVideoMaxFrameDuration)
conn.videoMaxFrameDuration = CMTimeMake(1, frameRate);
NSDictionary *videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
[videoOutput setVideoSettings:videoSettings];
[videoOutput setSampleBufferDelegate:self queue:capture_queue];
if ([captureSession canAddOutput:videoOutput])
[captureSession addOutput:videoOutput];
else
NSLog(#"Couldn't add video output");
[self.captureSession startRunning];
previewLayer.session = captureSession;