I have revisited AVCaptureSession in UIKit to capture a snapshot with the FaceTime camera. And my sample app will crash when AVCaptureSession starts running. Does anyone know how to fix it? The console says the following purple warning.
-[AVCaptureSession startRunning] should be called from background thread. Calling it on the main thread can lead to UI unresponsiveness
import UIKit
import AVFoundation
class CaptureViewController: UIViewController, AVCapturePhotoCaptureDelegate {
var captureSession: AVCaptureSession!
var cameraDevices: AVCaptureDevice!
var imagePhotoOutput: AVCapturePhotoOutput!
enum CameraCase {
case front
case back
}
// MARK: - IBAction
@IBAction func selectTapped(_ sender: UIButton) {
snapPicture()
}
// MARK: - Life cycle
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
prepareCamera(cameraCase: .front)
}
// MARK: - Camera
func prepareCamera(cameraCase: CameraCase) {
/* removing existing layers */
if let sublayers = self.view.layer.sublayers {
for sublayer in sublayers {
if sublayer.isKind(of: AVCaptureVideoPreviewLayer.self) {
sublayer.removeFromSuperlayer()
}
}
}
/* creating a capture session */
captureSession = AVCaptureSession()
if cameraCase == .front {
guard let device = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera], mediaType: AVMediaType.video, position: .back).devices.first else { return }
let videoInput = try? AVCaptureDeviceInput(device: device)
if captureSession.canAddInput(videoInput!) {
captureSession.addInput(videoInput!)
imagePhotoOutput = AVCapturePhotoOutput() // setting output destination
captureSession.addOutput(imagePhotoOutput) // adding photo output to session
}
} else {
guard let device = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera], mediaType: AVMediaType.video, position: .front).devices.first else { return }
let videoInput = try? AVCaptureDeviceInput(device: device)
if captureSession.canAddInput(videoInput!) {
captureSession.addInput(videoInput!)
imagePhotoOutput = AVCapturePhotoOutput() // setting output destination
captureSession.addOutput(imagePhotoOutput) // adding photo output to session
}
}
/* creating a capture layer */
let captureVideoLayer: AVCaptureVideoPreviewLayer = AVCaptureVideoPreviewLayer.init(session: captureSession)
captureVideoLayer.frame = CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height)
captureVideoLayer.videoGravity = AVLayerVideoGravity.resizeAspect
/* adding video capture layer to the view layer */
self.view.layer.addSublayer(captureVideoLayer)
/* starting capture session */
captureSession.startRunning() //<<<<<<<<<<<<<<<<<<<<<<<<<<< The console shows a purple warning here.
}
}
I've ended up with the following lines of code.
func prepareCamera(cameraCase: CameraCase) {
/* removing existing layers */
if let sublayers = self.view.layer.sublayers {
for sublayer in sublayers {
if sublayer.isKind(of: AVCaptureVideoPreviewLayer.self) {
sublayer.removeFromSuperlayer()
}
}
}
/* creating a capture session */
captureSession = AVCaptureSession()
guard let device = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera], mediaType: AVMediaType.video, position: cameraCase == .front ? .front : .back).devices.first else { return }
let videoInput = try? AVCaptureDeviceInput(device: device)
if captureSession.canAddInput(videoInput!) {
captureSession.addInput(videoInput!)
imagePhotoOutput = AVCapturePhotoOutput() // setting output destination
captureSession.addOutput(imagePhotoOutput) // adding photo output to session
}
/* creating a capture layer */
let previewLayer: AVCaptureVideoPreviewLayer = AVCaptureVideoPreviewLayer.init(session: captureSession)
previewLayer.videoGravity = AVLayerVideoGravity.resizeAspect
/* adding video capture layer to the view layer */
self.view.layer.addSublayer(previewLayer)
/* starting capture session */
DispatchQueue.global(qos: .background).async {
self.captureSession.startRunning()
}
}