Built-in webcam access in macOS

ViewController.swift

/* Tested in macOS Mojave (Dec 31, 2018) using Xcode 10.1
*  1. Create a new Xcode project 
*  2. Select macOS
*  3. Pick Cocoa App, give it a name, create
*  4. Open the project setting, click "Capabilities", goto "App Sandbox" -> "Hardware" -> check "Camera"
*  5. Open Info.plist of the project, and add row "Privacy - Camera Usage Description", give it some description
*  6. Open ViewController, and paste the code below
*  7. Click Play icon, give Cam access permissson "OK"
*  8. Voila! Preview screen!
*/
import Cocoa
import AVFoundation


class ViewController: NSViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        view.wantsLayer = true
        let session:AVCaptureSession = AVCaptureSession()
        session.sessionPreset = AVCaptureSession.Preset.low
        let device = AVCaptureDevice.default(for: .video)
        print("device found = ", device)
        let device_input : AVCaptureDeviceInput = try! AVCaptureDeviceInput(device: device!)
        
        
        let previewLayer:AVCaptureVideoPreviewLayer = AVCaptureVideoPreviewLayer(session: session)
        
        previewLayer.frame = view.bounds
        previewLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill
        self.view.layer?.addSublayer(previewLayer)
        if session.canAddInput(device_input)
        {
            session.addInput(device_input)
        }
        session.startRunning()
        
    }

    override var representedObject: Any? {
        didSet {
        // Update the view, if already loaded.
        }
    }
}