Video Buffer Output with Swift

My goal is to take the video buffer and ultimately convert it to NSData but I do not understand how to access the buffer properly. I have the captureOutput function but I have not been successful if converting the buffer and I'm not sure I am actually collecting anything in the buffer. This is all using swift code, I have found some examples using Objective-C but I am not able to understand the Obj-c code well enough to figure it out.

var captureDevice : AVCaptureDevice?
var videoCaptureOutput = AVCaptureVideoDataOutput()
var bounds: CGRect = UIScreen.mainScreen().bounds
let captureSession = AVCaptureSession()
var captureConnection: AVCaptureMovieFileOutput?


override func viewDidLoad() {
    super.viewDidLoad()
    captureSession.sessionPreset = AVCaptureSessionPreset640x480
    let devices = AVCaptureDevice.devices()

    for device in devices {
        if (device.hasMediaType(AVMediaTypeVideo)) {
            if device.position == AVCaptureDevicePosition.Back {
                captureDevice = device as? AVCaptureDevice
                if captureDevice != nil {
                    beginSession()
                }
            }
        }
    }
}

func beginSession() {
    var screenWidth:CGFloat = bounds.size.width
    var screenHeight:CGFloat = bounds.size.height
    var err : NSError? = nil
    captureSession.addInput(AVCaptureDeviceInput(device: captureDevice, error: &err)!)

    if err != nil {
        println("Error: \(err?.localizedDescription)")
    }

    videoCaptureOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey:kCVPixelFormatType_32BGRA]
    videoCaptureOutput.alwaysDiscardsLateVideoFrames = true


    captureSession.addOutput(videoCaptureOutput)


    videoCaptureOutput.setSampleBufferDelegate(self, queue: dispatch_queue_create("sample buffer delegate", DISPATCH_QUEUE_SERIAL))
    if captureSession.canAddOutput(self.videoCaptureOutput) {
        captureSession.addOutput(self.videoCaptureOutput)
    }

    func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, fromConnection connection: AVCaptureConnection!) {
      // I think this is where I can get the buffer info.

    }