如何使用AVCaptureVideoPreviewLayer从相机应用程序实现2倍缩放

使用AVCaptureVideoPreviewLayer从相机应用程序实现2倍缩放的步骤如下：

导入AVFoundation框架并引入相关头文件：

import AVFoundation

创建AVCaptureSession实例并设置输入设备（相机）：

let captureSession = AVCaptureSession()
guard let captureDevice = AVCaptureDevice.default(for: .video) else { return }
guard let input = try? AVCaptureDeviceInput(device: captureDevice) else { return }
captureSession.addInput(input)

创建AVCaptureVideoDataOutput实例并设置输出格式和代理：

let videoOutput = AVCaptureVideoDataOutput()
videoOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as String: kCVPixelFormatType_32BGRA]
videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue.global(qos: .default))
captureSession.addOutput(videoOutput)

创建AVCaptureVideoPreviewLayer实例并将其添加到视图层级中：

let previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
previewLayer.videoGravity = .resizeAspectFill
previewLayer.frame = view.bounds
view.layer.addSublayer(previewLayer)

启动AVCaptureSession：

captureSession.startRunning()

实现缩放功能：

func zoom(scale: CGFloat) {
    guard let captureDevice = AVCaptureDevice.default(for: .video) else { return }
    do {
        try captureDevice.lockForConfiguration()
        defer { captureDevice.unlockForConfiguration() }
        captureDevice.videoZoomFactor = scale
    } catch {
        print("Zoom failed: \(error.localizedDescription)")
    }
}

调用缩放方法实现2倍缩放：

zoom(scale: 2.0)

以上是使用AVCaptureVideoPreviewLayer从相机应用程序实现2倍缩放的基本步骤。AVCaptureVideoPreviewLayer用于显示相机捕获的实时视频预览，AVCaptureSession用于管理输入和输出设备的数据流。通过调整AVCaptureDevice的videoZoomFactor属性，可以实现相机的缩放功能。

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