如何使用 AVCaptureVideoPreviewLayer 从相机应用程序实现 2 倍变焦

我的应用程序中有一个 AVCaptureVideoPreviewLaye，它运行良好，并且显示与相机应用程序相同的预览视频。我想实现相机应用程序的 2 倍变焦功能。我该怎么做呢？

基本上，我希望我的预览层将视频源更改为与您在点击 1x 图标将其更改为 2x 时在相机应用程序中看到的比例相同。

设置预览层

func startSession(){
    captureSession = AVCaptureSession()
    captureSession?.sessionPreset = AVCaptureSessionPresetPhoto
    
    let backCamera = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
    
    // Catch error using the do catch block
    do {
        let input = try AVCaptureDeviceInput(device: backCamera)
        if (captureSession?.canAddInput(input) != nil){
            captureSession?.addInput(input)
            
            // Setup the preview layer
            previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
            previewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
            previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.portrait
            tempImageView.layer.addSublayer(previewLayer!)
            captureSession?.startRunning()
            
            // Set up AVCaptureVideoDataOutput
            let dataOutput = AVCaptureVideoDataOutput()
            dataOutput.videoSettings = [(kCVPixelBufferPixelFormatTypeKey as NSString) : NSNumber(value: kCVPixelFormatType_32BGRA as UInt32)]
            dataOutput.alwaysDiscardsLateVideoFrames = true
            
            if (captureSession?.canAddOutput(dataOutput) == true) {
                captureSession?.addOutput(dataOutput)
            }
            let queue = DispatchQueue(label: "com.bigbob.videoQueue")
            dataOutput.setSampleBufferDelegate(self, queue: queue)
        }
    } catch _ {
        print("Error setting up camera!")
    }

Set the videoZoomFactor你的AVCaptureDevice.defaultDevice预览图层的缩放也会随之变化。注意 Swift 4 现在被称为AVCaptureDevice.default.

do {
    try backCamera?.lockForConfiguration()
    let zoomFactor:CGFloat = 2
    backCamera?.videoZoomFactor = zoomFactor
    backCamera?.unlockForConfiguration()
} catch {
       //Catch error from lockForConfiguration
}