AVCaptureOutput Delegate

Question

I'm creating an application that is using -(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection { } function but that function is not being called. To furtherly explain, the application is using code from this tutorial to create a video recording app. When I ran the tutorial's code in xCode it ran the function above but when I copied it over into my application, not modifying it in anyway, it was never called.

Here's the code used:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSError *error = nil;
    AVCaptureSession *session = [[AVCaptureSession alloc] init];
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone){
        [session setSessionPreset:AVCaptureSessionPreset640x480];
    } else {
        [session setSessionPreset:AVCaptureSessionPresetPhoto];
    }
    // Select a video device, make an input
    AVCaptureDevice *device;
    AVCaptureDevicePosition desiredPosition = AVCaptureDevicePositionFront;
    // find the front facing camera
    for (AVCaptureDevice *d in [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]) {
        if ([d position] == desiredPosition) {
            device = d;
            isUsingFrontFacingCamera = YES;
            break;
        }
    }
    // fall back to the default camera.
    if( nil == device )
    {
        isUsingFrontFacingCamera = NO;
        device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    }
    // get the input device
    AVCaptureDeviceInput *deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
    if( !error ) {

        // add the input to the session
        if ( [session canAddInput:deviceInput] ){
            [session addInput:deviceInput];
        }

        previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
        previewLayer.backgroundColor = [[UIColor blackColor] CGColor];
        previewLayer.videoGravity = AVLayerVideoGravityResizeAspect;

        CALayer *rootLayer = [previewView layer];
        [rootLayer setMasksToBounds:YES];
        [previewLayer setFrame:[rootLayer bounds]];
        [rootLayer addSublayer:previewLayer];
        [session startRunning];

    }

    session = nil;

    if (error) {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:
                                  [NSString stringWithFormat:@"Failed with error %d", (int)[error code]]
                                                            message:[error localizedDescription]
                                                           delegate:nil
                                                  cancelButtonTitle:@"Dismiss"
                                                  otherButtonTitles:nil];
        [alertView show];
        [self teardownAVCapture];
    }

    NSDictionary *detectorOptions = [[NSDictionary alloc] initWithObjectsAndKeys:CIDetectorAccuracyLow, CIDetectorAccuracy, nil];
    faceDetector = [CIDetector detectorOfType:CIDetectorTypeFace context:nil options:detectorOptions];

    // Make a video data output
    videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
    // we want BGRA, both CoreGraphics and OpenGL work well with 'BGRA'
    NSDictionary *rgbOutputSettings = [NSDictionary dictionaryWithObject:
                                       [NSNumber numberWithInt:kCMPixelFormat_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
    [videoDataOutput setVideoSettings:rgbOutputSettings];
    [videoDataOutput setAlwaysDiscardsLateVideoFrames:YES]; // discard if the data output queue is blocked

    // create a serial dispatch queue used for the sample buffer delegate
    // a serial dispatch queue must be used to guarantee that video frames will be delivered in order
    // see the header doc for setSampleBufferDelegate:queue: for more information

    videoDataOutputQueue = dispatch_queue_create("VideoDataOutputQueue", DISPATCH_QUEUE_SERIAL);
    [videoDataOutput setSampleBufferDelegate:self queue:videoDataOutputQueue];
    if ( [session canAddOutput:videoDataOutput] ){
        [session addOutput:videoDataOutput];
    }

    // get the output for doing face detection.
    [[videoDataOutput connectionWithMediaType:AVMediaTypeVideo] setEnabled:YES];

    //[self setupCaptureSession];
}

Answer 1

Okay I think I know what the problem is. You had [session startRunning] even before you set up your videoDataOutput. A session with no video data output....well, will not call the AVCaptureOutput delegate.