需求：用macOS的摄像头作为二维码扫描器扫描二维码获取信息
基本流程：
1、创建session(捕捉会话)

let session = captureSession

2、创建设备

guard let videoDevice = AVCaptureDevice.default(for: .video) else {
print("No video device")
return
}

3、创建device input(捕捉设备输入)

guard let videoDeviceInput = try? AVCaptureDeviceInput(device: videoDevice),
session.canAddInput(videoDeviceInput)
else {
print("Unable to determine video device input")
return
}

4、预览view

self.layer = AVCaptureVideoPreviewLayer()

5、创建capture output(捕捉的输出)

let videoOutput = videoDataOutput

6、拍照、录视频、扫描二维码(从视频图像中选取某一帧画面，转化为图片，识别相应图片上的二维码)

具体代码：

let cameraPreview = CameraPreview()

fileprivate var captureSession = AVCaptureSession()

fileprivate var videoDataOutput = AVCaptureVideoDataOutput()

struct CameraManageView: View {
    
    @State var startMovieRunning = false
    
    var body: some View {
        VStack(alignment: .leading, spacing: nil){

            CameraPreviewHolder()
            
            Divider()
            Spacer()
            HStack(alignment: .center){

                Spacer()
                Button(action: {
                    print("二维码")
                    cameraPreview.scan()

                }, label: {
                    Text("二维码")
                }).padding()
                Spacer()
            }
        }
    }
}

struct CameraPreviewHolder: NSViewRepresentable{
    
    typealias NSViewType = CameraPreview

    func makeNSView(context: NSViewRepresentableContext<CameraPreviewHolder>) -> CameraPreview {

        let cameraPreview = CameraPreview()
        return cameraPreview
    }
    
    func updateNSView(_ nsView: CameraPreview, context: NSViewRepresentableContext<CameraPreviewHolder>) {
    }
}

final class CameraPreview: NSView {

    private var tmp:URL?
    
    init() {
        super.init(frame: .zero)
        
        var allowedAccess = false
        let blocker = DispatchGroup()
        blocker.enter()
        
        AVCaptureDevice.requestAccess(for: .video) { flag in
            allowedAccess = flag
            blocker.leave()
        }
        blocker.wait()

        guard allowedAccess else {
            print("No camera access")
            return
        }
        
        showCameraViewSeting()
    }
    
    func showCameraViewSeting() {

        let session = captureSession
        
        session.beginConfiguration()

        //分辨率
        session.sessionPreset = AVCaptureSession.Preset.high

        guard let videoDevice = AVCaptureDevice.default(for: .video) else {
            print("No video device")
            return
        }

        guard let videoDeviceInput = try? AVCaptureDeviceInput(device: videoDevice),
            session.canAddInput(videoDeviceInput)
            else {
            print("Unable to determine video device input")
            return
        }

        session.addInput(videoDeviceInput)

        let videoOutput = videoDataOutput
        videoOutput.alwaysDiscardsLateVideoFrames = true

        if session.canAddOutput(videoOutput) {
            session.addOutput(videoOutput)
        }

        session.commitConfiguration()
        captureSession = session
        
        self.wantsLayer = true
        
        self.layer = AVCaptureVideoPreviewLayer()
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    var videoPreviewLayer: AVCaptureVideoPreviewLayer {
        return self.layer as! AVCaptureVideoPreviewLayer
    }

    override func viewDidMoveToSuperview() { // on iOS .didMoveToSuperview
        super.viewDidMoveToSuperview()

        if nil != self.superview {
            self.videoPreviewLayer.session = captureSession
            self.videoPreviewLayer.videoGravity = .resizeAspect
            captureSession.startRunning()
        } else {
            captureSession.stopRunning()
        }
    }
    
    func scan(){
        videoDataOutput.setSampleBufferDelegate(cameraCaptureDelegate, queue: DispatchQueue.main)
    }

    func removeCameraPreview() {
        self.removeFromSuperview()
    }
}

class CameraCaptureDelegate: NSObject, AVCaptureVideoDataOutputSampleBufferDelegate{
    
    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {

        let cgImage:CGImage = imageFromSampleBuffer(sampleBuffer: sampleBuffer)
        print("\(cgImage)")
        
        //获取的图片经过EFQRCode（GitHub上搜这个库）识别，如果含有二维码，即可识别出二维码数据
//        let result = EFQRCode.recognize(image: cgImage)
//        print("didOutput : \(String(describing: result))")

    }

    func captureOutput(_ output: AVCaptureOutput, didDrop sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
        print("didDrop sampleBuffer")
    }
}

func imageFromSampleBuffer(sampleBuffer: CMSampleBuffer) -> CGImage {

    let imageBuffer: CVPixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
    let ciImage : CIImage = CIImage(cvPixelBuffer: imageBuffer)
    let context:CIContext = CIContext.init(options: nil)
    let cgImage:CGImage = context.createCGImage(ciImage, from: ciImage.extent)!

    return cgImage
}