Blur effect like iOS's facetime.

ViewController.Swift

class ViewController: UIViewController {
    
    
    var previewView : UIView!;
    var blurView: UIVisualEffectView!;
    
    //Camera Capture requiered properties
    var videoDataOutput: AVCaptureVideoDataOutput!
    var videoDataOutputQueue: DispatchQueue!
    var previewLayer:AVCaptureVideoPreviewLayer!
    var captureDevice : AVCaptureDevice!
    let session = AVCaptureSession()
    var currentFrame: CIImage!
    var done = false

    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        previewView = UIView(frame: CGRect(x: 0, y: 0, width:  UIScreen.main.bounds.size.width, height: UIScreen.main.bounds.size.height))
        previewView.contentMode = UIViewContentMode.scaleAspectFill
        view.addSubview(previewView)
        
        //Add a box view
        let commonBlurEffect = UIBlurEffect(style: .dark)
        blurView = UIVisualEffectView(effect: commonBlurEffect)
        blurView.frame = previewView.frame
        view.addSubview(blurView)
        self.setupAVCapture()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func viewWillAppear(_ animated: Bool) {
        if !done {
            session.startRunning()
        }
    }
    

    override var shouldAutorotate: Bool {
        if (UIDevice.current.orientation == UIDeviceOrientation.landscapeLeft ||
            UIDevice.current.orientation == UIDeviceOrientation.landscapeRight ||
            UIDevice.current.orientation == UIDeviceOrientation.unknown) {
            return false
        }
        else {
            return true
        }
    }
}

// AVCaptureVideoDataOutputSampleBufferDelegate protocol and related methods
extension ViewController:  AVCaptureVideoDataOutputSampleBufferDelegate{
    func setupAVCapture(){
        session.sessionPreset = .high
        guard let device = AVCaptureDevice
            .default(for: .video) else{
                            return
        }
        captureDevice = device
        beginSession()
        done = true
    }
    
    func beginSession(){
        var err : NSError? = nil
        var deviceInput:AVCaptureDeviceInput?
        do {
            deviceInput = try AVCaptureDeviceInput(device: captureDevice)
        } catch let error as NSError {
            err = error
            deviceInput = nil
        }
        if err != nil {
            print("error: \(String(describing: err?.localizedDescription))")
        }
        if self.session.canAddInput(deviceInput!){
            self.session.addInput(deviceInput!)
        }
        
        videoDataOutput = AVCaptureVideoDataOutput()
        videoDataOutput.alwaysDiscardsLateVideoFrames=true
        videoDataOutputQueue = DispatchQueue(label: "VideoDataOutputQueue")
        videoDataOutput.setSampleBufferDelegate(self, queue:self.videoDataOutputQueue)
        if session.canAddOutput(self.videoDataOutput){
            session.addOutput(self.videoDataOutput)
        }
        videoDataOutput.connection(with: AVMediaType.video)?.isEnabled = true
        
        self.previewLayer = AVCaptureVideoPreviewLayer(session: self.session)
        self.previewLayer.videoGravity = AVLayerVideoGravity.resizeAspect
        
        let rootLayer: CALayer = self.previewView.layer
        rootLayer.masksToBounds = true
        self.previewLayer.frame = rootLayer.bounds
        rootLayer.addSublayer(self.previewLayer)
        session.startRunning()
    }
    
    func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
        currentFrame =   self.convertImageFromCMSampleBufferRef(sampleBuffer)
    }
    
    
    // clean up AVCapture
    func stopCamera(){
        session.stopRunning()
        done = false
    }
    
    func convertImageFromCMSampleBufferRef(_ sampleBuffer:CMSampleBuffer) -> CIImage{
        let pixelBuffer: CVPixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
        let ciImage:CIImage = CIImage(cvImageBuffer: pixelBuffer)
        return ciImage
    }
}

preview