swift 3捕捉相机输出视频

Question

我有这个代码将设备上的后置摄像头连接到用户界面上的视图，我知道如何捕捉照片。如何从相机捕获视频并保存/重放视频，并改变我拍摄的视频的fps？

override func viewWillAppear(_ animated: Bool) {
    super.viewDidLoad()
    let deviceDiscoverySession = AVCaptureDeviceDiscoverySession(deviceTypes: [AVCaptureDeviceType.builtInDuoCamera, AVCaptureDeviceType.builtInTelephotoCamera,AVCaptureDeviceType.builtInWideAngleCamera], mediaType: AVMediaTypeVideo, position: AVCaptureDevicePosition.unspecified)
    for device in (deviceDiscoverySession?.devices)! {
        if (device as AnyObject).position == AVCaptureDevicePosition.back {
            do{
                let input = try AVCaptureDeviceInput(device: device )
                if captureSession.canAddInput(input){
                    captureSession.addInput(input)
                    if captureSession.canAddOutput(sessionOutput){
                        captureSession.addOutput(sessionOutput)
                        previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
                        previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
                        previewLayer.connection.videoOrientation = AVCaptureVideoOrientation.portrait
                        cameraView.layer.addSublayer(previewLayer)
                        captureSession.startRunning()
                    }
                }
            }
            catch{
                print("Error displaying camera data")
            }
        }
    }
}