Question

我正在使用AVFoundation扫描QRCode。通过各种教程，我想到了这段代码。一切正常，除了启动AVFoundation并将摄像机输出连接到所需的View时只有1秒的延迟。

import AVFoundation
import UIKit

protocol CameraControllerQRCodeDelegate {
    func qrCodefound(qrCodeValue : String,bounds: CGRect)
}

class CameraControllerQRCode :NSObject{

    //MARK: - Properties

    var delegate : CameraControllerQRCodeDelegate?

    var captureSession : AVCaptureSession?

    var frontCamera: AVCaptureDevice?
    var rearCamera : AVCaptureDevice?

    var currentCameraPosition : CameraPosition?
    var frontCameraInput : AVCaptureDeviceInput?
    var rearCameraInput : AVCaptureDeviceInput?

    var rearCaptureInput : AVCaptureInput?
    var captureOutput : AVCaptureOutput?

    var photoOutput : AVCapturePhotoOutput?
    var previewLayer : AVCaptureVideoPreviewLayer?

    var photoCaptureCompletionBlock : ((UIImage?,Error?) -> ())?

    enum CameraControllerError : Swift.Error{
        case captureSessionAlreadyRunning
        case captureSessionIsMissing
        case inputsAreInvalid
        case outputsAreInvalid
        case invalidOperation
        case noCamerasAvailable
        case torchCouldNotBeUsed
        case unableToFocus
        case unknown
    }

    public enum CameraPosition {
        case front
        case rear
    }

    //Body

    func prepare(completionHandler : @escaping (Error?) -> ()){

        func createCaptureSession(){
            self.captureSession = AVCaptureSession()
        }

        func configureCaptureDevices() throws {

            let session = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera], mediaType: .video, position: .back)

            let cameras = session.devices
            if cameras.isEmpty { throw CameraControllerError.noCamerasAvailable }

            for camera in cameras{

                print(camera.deviceType.rawValue)
                if camera.position == .front {
                    self.frontCamera = camera
                }

                if camera.position == .back {
                    self.rearCamera = camera

                    try camera.lockForConfiguration()
                    camera.focusMode = .continuousAutoFocus
                    camera.unlockForConfiguration()
                    print(camera.activeVideoMaxFrameDuration)
                }
            }

        }

        func configureDeviceInputs() throws {
            guard let captureSession = self.captureSession else { throw CameraControllerError.captureSessionIsMissing}

            if let rearCamera = self.rearCamera {
                self.rearCameraInput = try AVCaptureDeviceInput(device: rearCamera)
                self.rearCaptureInput = try AVCaptureDeviceInput(device: rearCamera)

                if captureSession.canAddInput(self.rearCameraInput!){
                    captureSession.addInput(self.rearCameraInput!)
                }else{
                    throw CameraControllerError.inputsAreInvalid
                }

                self.currentCameraPosition = .rear

            }else if let frontCamera = self.frontCamera {
                self.frontCameraInput = try AVCaptureDeviceInput(device: frontCamera)

                if captureSession.canAddInput(self.frontCameraInput!){
                    captureSession.addInput(self.frontCameraInput!)
                }else{
                    throw CameraControllerError.inputsAreInvalid
                }
                self.currentCameraPosition = .front
            }else{
                throw CameraControllerError.noCamerasAvailable
            }
        }

        func configurePhotoOutput() throws {
            guard let captureSession = self.captureSession else {
                throw CameraControllerError.captureSessionIsMissing
            }

            self.photoOutput = AVCapturePhotoOutput()
            self.photoOutput!.setPreparedPhotoSettingsArray([AVCapturePhotoSettings(format: [AVVideoCodecKey:AVVideoCodecType.jpeg])], completionHandler: nil)

            if captureSession.canAddOutput(self.photoOutput!){
                captureSession.addOutput(self.photoOutput!)
            }

            //metadataOutput

            let metadataOutput = AVCaptureMetadataOutput()

            if captureSession.canAddOutput(metadataOutput){
                captureSession.addOutput(metadataOutput)
                metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
                metadataOutput.metadataObjectTypes = [.qr]
            }else{
                throw CameraControllerError.outputsAreInvalid
            }

            captureSession.startRunning()
        }

        DispatchQueue(label: "prepare").async {
            do{
                createCaptureSession()
                try configureCaptureDevices()
                try configureDeviceInputs()
                try configurePhotoOutput()
            }catch{
                DispatchQueue.main.async {
                    completionHandler(error)
                }
                return
            }

            DispatchQueue.main.async {
                completionHandler(nil)
            }

        }

    }

    func displayPreview(on view : UIView) throws {
        guard let captureSession = self.captureSession,captureSession.isRunning else {
            throw CameraControllerError.captureSessionIsMissing
        }

        self.previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        guard let previewLayer = self.previewLayer else {
            throw CameraControllerError.unknown
        }
        previewLayer.videoGravity = .resizeAspectFill
        previewLayer.connection?.videoOrientation = .portrait
        view.layer.insertSublayer(previewLayer, at: 0)
        previewLayer.frame = view.frame

    }





    //Added Code to CameraControllerQRCode
    func removePreviewLayer()throws{
        guard let previewLayer = self.previewLayer else {
            throw CameraControllerError.unknown
            return
        }

        previewLayer.removeFromSuperlayer()
    }


    func toggle(on:Bool)throws{
        guard let device = AVCaptureDevice.default(for: .video) else {
            throw CameraControllerError.torchCouldNotBeUsed
        }

        if device.hasTorch{
            do{
                try device.lockForConfiguration()

                if on == true{
                    device.torchMode = .on
                }else{
                    device.torchMode = .off
                }
                device.unlockForConfiguration()
            }catch{
                throw CameraControllerError.torchCouldNotBeUsed
            }
        }else{
            throw CameraControllerError.torchCouldNotBeUsed
        }
    }

    func autofocus(focusPoint : CGPoint)throws{
        if let device = rearCamera{
            do{
                try device.lockForConfiguration()
                device.isFocusModeSupported(.continuousAutoFocus)
                device.focusPointOfInterest = focusPoint
                device.focusMode = .autoFocus
                device.exposurePointOfInterest = focusPoint

                device.exposureMode = .continuousAutoExposure
                device.unlockForConfiguration()
            }catch{
                throw CameraControllerError.unableToFocus
            }
        }
    }

}

extension CameraControllerQRCode : AVCaptureMetadataOutputObjectsDelegate{

    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {

        guard let captureSession = captureSession ,captureSession.isRunning else {
            print("CaptureSession nil")
            return
        }

        guard !metadataObjects.isEmpty else {
            return
        }

        guard let metadataObject = metadataObjects[0] as? AVMetadataMachineReadableCodeObject else {
            print("Error Delegate method 1")
            return
        }

        let qrCodeBounds = metadataObject.bounds

        guard let QRCodeRect = previewLayer?.layerRectConverted(fromMetadataOutputRect: qrCodeBounds) else{
            return
        }

        guard let stringValue = metadataObject.stringValue else {
            return
        }

        guard let delegate = delegate else {
            print("Delegate : nil")
            return
        }

        delegate.qrCodefound(qrCodeValue: stringValue, bounds: QRCodeRect)


    }
}

使用prepare()然后使用displayPreview(on:)

时会出现问题

最长需要1-2秒才能开始显示实际的相机输出。

这是AVFoundation的理想行为吗？

非常感谢

Answer 1

是的，需要一段时间。我的代码也需要约1秒钟的时间。 Tbf，Viber的QR扫描会立即加载，因此可能有一种方法可以“移除”（摊销-提前启动AVCapturSession吗？）加载时间

相机需要1秒钟才能开始使用AVFoundation

1 个答案: