Snippet showing how to capture QR codes from the device camera on iOS or Mac OS X

QRCodeScanner.m

- (BOOL) startCapture: (NSError**)outError {
    if (!_session) {
        _session = [[AVCaptureSession alloc] init];
        AVCaptureDevice* video = [AVCaptureDevice defaultDeviceWithMediaType: AVMediaTypeVideo];
        if (!video)
            return [self failWithMessage: @"No video camera available" error: outError];
        AVCaptureDeviceInput* input = [AVCaptureDeviceInput deviceInputWithDevice: video
                                                                            error: outError];
        if (!input)
            return [self failWithMessage: @"Couldn't acquire input device" error: outError];
        [_session addInput: input];

        AVCaptureVideoDataOutput* output = [[AVCaptureVideoDataOutput alloc] init];
        output.alwaysDiscardsLateVideoFrames = YES;
        [output setSampleBufferDelegate: self queue: dispatch_get_main_queue()];
        [_session addOutput: output];

        NSLog(@"Starting video capture...");
        [[NSNotificationCenter defaultCenter] addObserver: self
                                                 selector: @selector(sessionNotification:)
                                                     name: nil // all notifications
                                                   object: _session];
        [_session startRunning];
    }
    if (!_qrDetector) {
        _qrDetector = [CIDetector detectorOfType: CIDetectorTypeQRCode
                                         context: nil
                                         options: nil];
    }
    return YES;
}


- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
       fromConnection:(AVCaptureConnection *)connection
{
    CVImageBufferRef imageBuf = CMSampleBufferGetImageBuffer(sampleBuffer);
    CIImage* frame = [CIImage imageWithCVImageBuffer: imageBuf];
    CFAbsoluteTime time = CFAbsoluteTimeGetCurrent();
    if (time - _lastScanTime >= kMinScanInterval) {
        _lastScanTime = time;
        self.scannedFeature = (CIQRCodeFeature*)[_qrDetector featuresInImage: frame].firstObject;
    }
    self.currentFrame = frame;
    NSString* message = [self.scannedFeature.messageString copy];
    if (message && ![message isEqualToString: _scannedString]) {
        self.scannedString = message;
    }
}