Barcode on swift 4

I'm trying to upgrade mi app to swift 4, but the barcode reader is not working.

I have isolated the barcode reader code, and still not working. The camera works but it does not detect the barcode.

The code worked just fine on swift 3 iOS 10.

This is the complete code

import AVFoundation
import UIKit

class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
var captureSession: AVCaptureSession!
var previewLayer: AVCaptureVideoPreviewLayer!

override func viewDidLoad() {
    super.viewDidLoad()

    view.backgroundColor = UIColor.black
    captureSession = AVCaptureSession()

    let videoCaptureDevice = AVCaptureDevice.default(for: AVMediaType.video)
    let videoInput: AVCaptureDeviceInput

    do {
        videoInput = try AVCaptureDeviceInput(device: videoCaptureDevice!)
    } catch {
        return
    }

    if (captureSession.canAddInput(videoInput)) {
        captureSession.addInput(videoInput)
    } else {
        failed();
        return;
    }

    let metadataOutput = AVCaptureMetadataOutput()

    if (captureSession.canAddOutput(metadataOutput)) {
        captureSession.addOutput(metadataOutput)

        metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        metadataOutput.metadataObjectTypes = [AVMetadataObject.ObjectType.ean8, AVMetadataObject.ObjectType.ean13, AVMetadataObject.ObjectType.pdf417]
    } else {
        failed()
        return
    }

    previewLayer = AVCaptureVideoPreviewLayer(session: captureSession);
    previewLayer.frame = view.layer.bounds;
    previewLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill;
    view.layer.addSublayer(previewLayer);

    captureSession.startRunning();
}

func failed() {
    let ac = UIAlertController(title: "Scanning not supported", message: "Your device does not support scanning a code from an item. Please use a device with a camera.", preferredStyle: .alert)
    ac.addAction(UIAlertAction(title: "OK", style: .default))
    present(ac, animated: true)
    captureSession = nil
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    if (captureSession?.isRunning == false) {
        captureSession.startRunning();
    }
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)

    if (captureSession?.isRunning == true) {
        captureSession.stopRunning();
    }
}

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {
    captureSession.stopRunning()

    if let metadataObject = metadataObjects.first {
        let readableObject = metadataObject as! AVMetadataMachineReadableCodeObject;

        AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
        found(code: readableObject.stringValue!);
    }

    dismiss(animated: true)
}

func found(code: String) {
    print(code)
}

override var prefersStatusBarHidden: Bool {
    return true
}

override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
    return .portrait
}
}

I am using iOS 11 on my iPhone, upgraded to beta 9.

Any idea? Thank you.