AVCaptureVideoPreviewLayer 的比例

Question

我目前正在 Swift 应用程序中处理 QR 扫描视图。我想将 VideoPreview 居中放置在我的视图中间。

视图如下所示：

视图（白色）称为 ScanView，我想使图像预览与 ScanView 大小相同并将其居中。

代码片段：

感谢您的帮助！

Answer 1

这是一个可行的解决方案：

import UIKit
import AVFoundation

class ViewController: UIViewController, AVCaptureVideoDataOutputSampleBufferDelegate, AVCaptureMetadataOutputObjectsDelegate {
  @IBOutlet weak var innerView: UIView!
  var session: AVCaptureSession?
  var input: AVCaptureDeviceInput?
  var previewLayer: AVCaptureVideoPreviewLayer?
    
  override func viewDidLoad() {
    super.viewDidLoad()
    createSession()
  }
    
  override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    self.previewLayer?.frame.size = self.innerView.frame.size
  }
    
  private func createSession() {
    do {
      self.session = AVCaptureSession()
      if let device = AVCaptureDevice.default(for: AVMediaType.video) {
        self.input = try AVCaptureDeviceInput(device: device)
        self.session?.addInput(self.input!)
        self.previewLayer = AVCaptureVideoPreviewLayer(session: self.session!)
        self.previewLayer?.frame.size = self.innerView.frame.size
        self.previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        self.innerView.layer.addSublayer(self.previewLayer!)

        //______ 1. solution with Video camera ______//
        let videoOutput = AVCaptureVideoDataOutput()
        videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue.main)
        self.session?.canAddOutput(videoOutput)
        self.session?.addOutput(videoOutput)
        self.session?.startRunning()

        //______ 2. solution with QR code ______//
        let videoOutput = AVCaptureMetadataOutput()
        videoOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        self.session?.canAddOutput(videoOutput)
        self.session?.addOutput(videoOutput)
        // explanation here: 
        videoOutput.metadataObjectTypes = [AVMetadataObject.ObjectType.qr]
        self.session?.startRunning()
      }
    } catch _ {
    }
  }

  //MARK: AVCaptureVideoDataOutputSampleBufferDelegate
  public func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
    if let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) {
        let cameraImage = CIImage(cvPixelBuffer: pixelBuffer)
        // awesome stuff here
    }
  }

  //MARK: AVCaptureMetadataOutputObjectsDelegate
  func setMetadataObjectsDelegate(_ objectsDelegate: AVCaptureMetadataOutputObjectsDelegate?, queue objectsCallbackQueue: DispatchQueue?) {
    
  }
}

要求：

设置：Privacy - Camera Usage Description
innerView 必须初始化，我用 Storyboard 做的有以下限制：

这里是结果：

Answer 2

我和Philip Dz有同样的问题。最后通过将 setupVideo() 函数从 viewDidLoad 移动到 viewDidAppear:

来解决问题

在 viewDidLoad 中调用 setupVideo()

在 viewDidAppear 中调用 setupVideo():

Answer 3

也许我有点晚了，但我刚刚实现了 QRScanner，并且根据设备运行可以缩放视频流。这是通过 AVCaptureDevice.videoZoomFactor 属性实现的。所以，为了增强小方QRScanner的用户体验，可以稍微修改上面的代码，在self.session?.startRunning()

之前插入下面一行device.zoomFactor = min(YOUR_ZOOM_FACTOR_VALUE, device.activeFormat.videoMaxZoomFactor)

AVCaptureVideoPreviewLayer 的比例

Scale of AVCaptureVideoPreviewLayer

video

preview

avfoundation

ios

swift