SnapChat Desktop应用中的AVCaptureDevice不抛出视频提要

Question

Snapchat刚刚发布了一个桌面应用（link），该应用旨在在系统中创建视频设备，供任何视频应用（例如Skype，Google Hangouts，苹果公司的Photobooth甚至OBS）用于实时流传输。它在其他应用中效果很好，因为它们似乎可以与“ FaceTime HD摄像头”一起检测摄像头设备。

因此，我尝试使用Xcode制作OSX应用程序。希望我能得到视频提要。我使用的是我从此github取得的以下代码示例：AcceCamera Demo

该应用程序非常适合显示“ FacetimeHD摄像机”的提要，但在选择SnapCam设备时不起作用（因为它没有显示任何内容）。

这是代码（您也可以使用上面的链接，与此唯一的区别是选择SnapCam设备）：

import Cocoa
import AVFoundation

class ViewController: NSViewController {

    @IBOutlet weak var camera: NSView!

    let captureSession = AVCaptureSession()
    var captureDevice : AVCaptureDevice?
    var previewLayer : AVCaptureVideoPreviewLayer?

    override func viewDidLoad() {
        super.viewDidLoad()

        camera.layer = CALayer()


        // Do any additional setup after loading the view, typically from a nib.
        captureSession.sessionPreset = AVCaptureSessionPresetLow

        // Get all audio and video devices on this machine
        let devices = AVCaptureDevice.devices()

        // Find the FaceTime HD camera object
        for device in devices! {
//            print(device)

            // Camera object found and assign it to captureDevice
            if ((device as AnyObject).hasMediaType(AVMediaTypeVideo)) {
                print(device)
                let d = device as? AVCaptureDevice
                print("\(d?.manufacturer)")
                if(d?.manufacturer == "SnapVendor"){
                    captureDevice = device as? AVCaptureDevice
                    break;
                }

            }
        }


        if captureDevice != nil {

            do {

                try captureSession.addInput(AVCaptureDeviceInput(device: captureDevice))
                previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
                previewLayer?.frame = (self.camera.layer?.frame)!

                // Add previewLayer into custom view
                self.camera.layer?.addSublayer(previewLayer!)

                // Start camera
                captureSession.startRunning()

            } catch {
                print(AVCaptureSessionErrorKey.description)
            }
        }


    }

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


}

我觉得很奇怪，OBS等其他应用程序在接收提要时没有问题。