How to access Mac default camera using swift xcode

In your code the

self.view.layer?.addSublayer(previewLayer)

will not be executed since self.view.layer is nil so that won't be executed.

Alas, this does not seem to be only issue since even when adding a layer the camera does not start working. You will likely have to dig into this:

https://developer.apple.com/library/mac/samplecode/AVRecorder/Introduction/Intro.html

Be sure to check that your view has a Core Animation Layer in IB:

Working code in swift 5.

import Cocoa
import AVFoundation

class SomwViewController: NSViewController {
    @IBOutlet private var cameraView: NSView?
    let session: AVCaptureSession = AVCaptureSession()

    override func viewDidLoad() {
        super.viewDidLoad()
        cameraView?.wantsLayer = true
        cameraView?.layer?.backgroundColor = NSColor.black.cgColor
        session.sessionPreset = AVCaptureSession.Preset.low
        let input: AVCaptureInput = try! AVCaptureDeviceInput(device: AVCaptureDevice.default(for: .video)!)
        session.addInput(input)
        let previewLayer: AVCaptureVideoPreviewLayer = AVCaptureVideoPreviewLayer(session: session)
        previewLayer.frame = cameraView!.bounds
        previewLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill

        cameraView?.layer?.addSublayer(previewLayer)
    }

    override func viewDidAppear() {
        session.startRunning()
    }

    override func viewDidDisappear() {
        session.stopRunning()
    }
}

You should definitely not use force unwraps, it's just an example.