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!
");
        DispatchQueue.main.async(execute: {
            // Do stuff
        })
    }
}

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

user_348114 · Answer

I had a similar issue, however my issue was due to the way I was creating the AVCaptureSession.

I had opted to create the AVCaptureSession in a function and return it to the caller, this part is fine, however, I neglected to hold a reference to the session in a class variable which was causing the AVCaptureSession to go out of scope and be collected by ARC before the delegate could get invoked.

Once I set the class variable so that the AVCaptureSession wasn't released when the calling function exited everything started to work.

Wanted to share just in case someone else ran into the same issue.

user_4172423 · Answer

If previous answers cannot solve your problem for swift 4 and newer, correct the function name by add public can fix the problem.

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

user_2083179 · Answer

The problem got fixed when i changed dualCamera to AVCaptureDeviceType.builtInWideAngleCamera swift 4. Hope it helps anyone in need.

captureOutput function isn't called using setSampleBufferDelegate

6 Answers