captureOutput function isn't called using setSampleBufferDelegate

Question

I'm starting to develop an iOS app and this is my first SO post. I'm trying to implement a UI view which can show the preview video of the rear camera and process the captured frames. My preview layer works perfectly and I can see the picture display in my UI view. However, the captureOutput function is never called.

I have searched online for silimar issues and solutions for a while and tried to tweak different things including the output, connection, and dispatch queue settings, but none has worked. Can anyone help me out or share some insights and directions? Thanks a lot in advance!

Here is my code, I'm using Xcode 11 beta with iOS 10 as build target.

class ThreeDScanningViewController: UIViewController, 
AVCaptureVideoDataOutputSampleBufferDelegate {

    @IBOutlet weak var imageView: UIImageView!

    var session : AVCaptureSession!
    var device : AVCaptureDevice!
    var output : AVCaptureVideoDataOutput!
    var previewLayer : AVCaptureVideoPreviewLayer!

    override func viewDidLoad() {
        super.viewDidLoad()
                //NotificationCenter.default.addObserver(self, selector: #selector(self.startedNotif), name: NSNotification.name.CaptureSessionDidStartRunningNotification, object: nil)

    func initCamera() -> Bool {
        session = AVCaptureSession()
        session.sessionPreset = AVCaptureSession.Preset.medium

        let devices = AVCaptureDevice.devices()

        for d in devices { 
            if ((d as AnyObject).position == AVCaptureDevice.Position.back) {
                device = d as! AVCaptureDevice
            }
        }
        if device == nil {
            return false
        }

        do {
            // Set up the input

            let input : AVCaptureDeviceInput!
            try input = AVCaptureDeviceInput(device: device)

            if session.canAddInput(input) {
                session.addInput(input)
            } else {
                return false
            }

            // Set up the device

            try device.lockForConfiguration()
            device.activeVideoMinFrameDuration = CMTimeMake(1, 15)
            device.unlockForConfiguration()

            // Set up the preview layer

            previewLayer = AVCaptureVideoPreviewLayer(session: session)
            previewLayer.frame = imageView.bounds
            imageView.layer.addSublayer(previewLayer)

            // Set up the output

            output = AVCaptureVideoDataOutput()
            output.videoSettings = [(kCVPixelBufferPixelFormatTypeKey as NSString) as String: kCVPixelFormatType_32BGRA]

            let queue = DispatchQueue(label: "myqueue")
            output!.setSampleBufferDelegate(self, queue: queue)

            output.alwaysDiscardsLateVideoFrames = true

            if session.canAddOutput(output) {
                session.addOutput(output)
            } else {
                return false
            }

            for connection in output.connections {
                if let conn = connection as? AVCaptureConnection {
                    if conn.isVideoOrientationSupported {
                        conn.videoOrientation = AVCaptureVideoOrientation.portrait
                    }
                }
            }

            session.startRunning()

        } catch let error as NSError {
            print(error)
            return false
        }

        return true
    }

    func captureOutput (captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
        print("captureOutput!\n");
        DispatchQueue.main.async(execute: {
            // Do stuff
        })
    }
}

Here are some links I've looked into, none is relevant to solve my issue:

• AVCaptureVideoDataOutput captureOutput not being called

• ios capturing image using AVFramework

• AVCaptureDeviceOutput not calling delegate method captureOutput

• iOS: captureOutput:didOutputSampleBuffer:fromConnection is NOT called

• didOutputSampleBuffer delegate not called

Answer 1

I have finally managed to find the cause of the issue. You need to make sure to use the correct function signature for the captureOutput function for the Swift 3 syntax.

func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection)

NOT

func captureOutput(_ output: AVCaptureOutput, didOutputSampleBuffer sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection)

I was using older version of the Swift syntax and the compiler did not warn me of the issue! After correcting the function signatures, the captureOutput function gets called beautifully:-)

Answer 2

From Swift 4:

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

won't be called as it no longer exists.

It has been changed to the following :

func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection)