学习MacOS App (Part 6: Camera Preview)

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通过AV Foundation来实现摄像头的preview, 下面的代码直接用了当前View对应的layer，也可以加入一个Custom关联上去，一个道理。PreviewLayer只需要有session就行，所以这里就没有关联output，后面我们会来介绍。

func setup() {
    // Create a capture session
    session = AVCaptureSession()
    session.sessionPreset = .hd1280x720
    
    // Get a refenerce to the default camera
    let videoDevice =  AVCaptureDevice.default(for: .video)
    
    // Create a device input for the camera
    guard
        let videoInput = try? AVCaptureDeviceInput(device: videoDevice!),
        session.canAddInput(videoInput)
    else {
        print("### input FAILED")
        return
    }
    
    // Connect the input to the session
    session.addInput(videoInput)
    
    let previewLayer = AVCaptureVideoPreviewLayer.init(session: session)
    previewLayer.videoGravity = .resizeAspectFill
    
    self.view.layer = previewLayer
    
    session.startRunning()
    print("### setup OK")
}

参考:

• AV Foundation 秘籍
• Setting Up a Capture Session | Apple Developer Documentation
• iOS - 视频采集详解 | LinXunFeng‘s Blog
• ObjC 中国 - iOS 上的相机捕捉

MacOS提供的AVCaptureScreenInput可以很方便的采集屏幕，

// enumerate screens
for each in NSScreen.screens {
    print("\(each.localizedName), \(each.displayID!)")
}

// Create a capture session
session = AVCaptureSession()
session.sessionPreset = .hd1280x720

let screenInput = AVCaptureScreenInput(displayID: NSScreen.main?.displayID ?? 1)

AVCaptureVideoDataOutput

前面通过AVCaptureVideoPreviewLayer来渲染直接预览，但如果我们需要对buffer做拦截，比如灰度或者美颜，这时就需要用到data output.

class ViewController: NSViewController, AVCaptureVideoDataOutputSampleBufferDelegate {
    var session : AVCaptureSession!
    var bufferDisplayLayer: AVSampleBufferDisplayLayer!

    override func viewDidLoad() {
        super.viewDidLoad()
        bufferDisplayLayer = AVSampleBufferDisplayLayer()
        setupCamera()
    }

    func setupCamera() {
        // Create a capture session
        session = AVCaptureSession()
        session.sessionPreset = .hd1280x720
        
        // Get a refenerce to the default camera
        let videoDevice =  AVCaptureDevice.default(for: .video)
        
        // Create a device input for the camera
        guard
            let videoInput = try? AVCaptureDeviceInput(device: videoDevice!),
            session.canAddInput(videoInput)
        else {
            print("### input FAILED")
            return
        }
        
        // Connect the input to the session
        session.addInput(videoInput)
        
        let dataOutput = AVCaptureVideoDataOutput()
        dataOutput.setSampleBufferDelegate(self, queue: DispatchQueue.global())
        if(session.canAddOutput(dataOutput)) {
            session.addOutput(dataOutput)
        }
        
        // Link layer
        bufferDisplayLayer.videoGravity = .resizeAspectFill
        self.view.layer = bufferDisplayLayer;
        
        session.startRunning()
        print("### setup OK")
    }
    
    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
        bufferDisplayLayer.enqueue(sampleBuffer)
    }
}

后面我们继续看滤镜效果。