Web不能出现在AVCaptureDevice.devices（）中

Question

我正在尝试使用适用于Mac应用程序的网络摄像头获取用户照片，问题是当我使用AVCaptureDevice.devices（）请求设备列表时，API返回0项，但是网络摄像头可在FaceTime和在Skype中。

    @IBOutlet private weak var imageView: NSImageView!

    let session = AVCaptureSession()
    let devices = AVCaptureDevice.devices()

    guard !devices.isEmpty else {
        print(devices.count)
        print("No device")
        return
    }

    for device in devices {
        print(device.localizedName)
    }

    if let device = devices.first {
        do {
            let input = try AVCaptureDeviceInput(device:device)
            session.addInput(input)
            let output = AVCaptureStillImageOutput()
            output.outputSettings = [AVVideoCodecKey: AVVideoCodecType.jpeg]
            session.addOutput(output)

            if let connection = output.connection(with: AVMediaType.video) {
                output.captureStillImageAsynchronously(from: connection) { (returnedBuffer, error) in
                    guard error == nil else {
                        print(error!.localizedDescription)
                        return
                    }
                    guard let buffer = returnedBuffer else {
                        return
                    }
                    guard let data = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(buffer) else {
                        return
                    }

                    if let image = NSImage(data: data) {
                        DispatchQueue.main.async {
                            self.imageView.image = image
                        }
                    }
                }
            }

        } catch {
            print(error.localizedDescription)
        }
    }
}