设置 `device.activeVideoMinFrameDuration` 和 `device.activeVideoMaxFrameDuration` 没有任何作用

Question

我正在制作一个自定义的相机应用程序，我想以 60fps 的速度获取相机输入（我不太关心质量）并在 UIView 中显示它。

到目前为止我有以下内容：

struct CustomCameraView: UIViewRepresentable {
    func makeUIView(context: Context) -> some UIView {
        let previewView = UIImageView()
        func configureCameraForHighestFrameRate(device: AVCaptureDevice) {
            do {
                try device.lockForConfiguration()                
                let fr = CMTimeMake(value: 1, timescale: 60)
                device.activeVideoMinFrameDuration = fr
                device.activeVideoMaxFrameDuration = fr                
                device.unlockForConfiguration()
            } catch {
                print("error setting frame rate")
            }
        }
        
        func setupLivePreview() {
            videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
            videoPreviewLayer.videoGravity = .resizeAspect
            videoPreviewLayer.connection?.videoOrientation = .portrait
            previewView.layer.addSublayer(videoPreviewLayer)
            captureSession.commitConfiguration()
            DispatchQueue.global(qos: .userInitiated).async {
                captureSession.startRunning()
                DispatchQueue.main.async {
                    videoPreviewLayer.frame = previewView.bounds
                }
            }
        }
                
        var captureSession: AVCaptureSession!
        var videoPreviewLayer: AVCaptureVideoPreviewLayer!
        
        captureSession = AVCaptureSession()
        captureSession.beginConfiguration()        
        guard let backCamera = AVCaptureDevice.default(for: AVMediaType.video) else {
            print("Unable to access back camera!")
            return UIImageView()
        }        
        configureCameraForHighestFrameRate(device: backCamera)
        do {
            let input = try AVCaptureDeviceInput(device: backCamera)
            print("max frame duration on input",
input.device.activeVideoMaxFrameDuration)
            
            if captureSession.canAddInput(input) {
                captureSession.addInput(input)
                setupLivePreview()
            }
        }
        catch let error  {
            print("Error Unable to initialize back camera:  \(error.localizedDescription)")
        }
        
        return previewView
    }

    func updateUIView(_ uiView: UIViewType, context: Context) {}
}

很简单，我访问相机，设置它的 activeVideoMinFrameDuration 和 activeVideoMaxFrameDuration，然后我使用 AVCaptureVideoPreviewLayer 替换 UIImageView 的 CALayer.

我尝试将 CMTime 的 timescale 更改为 30、20、10，甚至 1，但它没有有什么作用。我该怎么办？

我没有收到任何错误，这是我的系统信息：

iPhone 11 专业版
XCode 版本 12.0.1 (12A7300)
iOS 14.0.1

Answer 1

原来Apple's documentation是错误的：

Directly configuring a capture device’s activeFormat property changes the capture session’s preset to inputPriority.

这不是真的，我必须将捕获会话的预设设置为 .inputPriority 才能对捕获的设备进行配置。所以添加这一行解决了问题：

captureSession.sessionPreset = .inputPriority

我在 Apple 开发者论坛上做了 a post，希望他们能看一看。

设置 `device.activeVideoMinFrameDuration` 和 `device.activeVideoMaxFrameDuration` 没有任何作用

Setting `device.activeVideoMinFrameDuration` and `device.activeVideoMaxFrameDuration` doesn't do anything

iphone

ios

swift

swiftui