如何在摄像头应用程序中使用AVCaptureVideoPreviewLayer实现2倍缩放

Question

我在我的应用程序中有一个AVCaptureVideoPreviewLayer，它运行良好，并显示与相机应用程序相同的预览视频。我想要实现相机应用程序的2倍变焦功能。如何做到这一点？

基本上，我希望我的预览图层将视频源更改为您在相机应用程序中点击1x图标切换到2x时所看到的比例。

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!")
    }

- Lightsout

Answer 1

设置AVCaptureDevice.defaultDevice的videoZoomFactor属性，预览图层的缩放比例也会随之改变。注意，在Swift 4中，它现在被称为AVCaptureDevice.default。

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

- Lightsout

Answer 2

这是一个更新的答案，它先检查缩放因子是否可用，然后再尝试设置它。这将防止可能不必要的异常捕获，并且您可以轻松地使用一个变量调整缩放检查和设置。

if let captureDevice = AVCaptureDevice.default(for: AVMediaType.video) {
    let zoomFactor : CGFloat = 2
    if (captureDevice.maxAvailableVideoZoomFactor >= zoomFactor) {
        try? captureDevice.lockForConfiguration()
        captureDevice.videoZoomFactor = zoomFactor
        captureDevice.unlockForConfiguration()
    }
}

- Ethan Allen