Swift使用AVFoundation实现自定义相机

1.什么是AVFoundation

AV Foundation是在iOS，macOS，watchOS和tvOS上使用基于时间的视听媒体的全功能框架。例如，你可以用它来检查，创建，编辑或重新编码媒体文件。您也可以从设备得到输入流和在实时捕捉回放过程中操控视频。

2.为什么使用AVFoundation

通常情况下，如果需要播放视频，可以使用AVKit框架,如果需要拍照或者录制视频则可以使用UIKit中的UIImagePickerController实现，但是如果你想要更多自定义的功能时，例如，以编程方式更改硬件参数，或者操纵实时预览图,就需要使用到AVFoundation来实现,本文介绍如何通过AVFoundation来实现自定义相机。

3.AVFoundation 相关类

AVFoundation 框架基于以下几个类实现图像捕捉 ，通过这些类可以访问来自相机设备的原始数据并控制它的组件:
AVCaptureDevice 是关于相机硬件的接口。它被用于控制硬件特性，诸如镜头的位置、曝光、闪光灯等。
AVCaptureDeviceInput 提供来自设备的数据。
AVCaptureOutput 是一个抽象类，描述 capture session 的结果。以下是三种关于静态图片捕捉的具体子类：
AVCaptureStillImageOutput 用于捕捉静态图片
AVCaptureMetadataOutput 启用检测人脸和二维码
AVCaptureVideoOutput 为实时预览图提供原始帧
AVCaptureSession 管理输入与输出之间的数据流，以及在出现问题时生成运行时错误。
AVCaptureVideoPreviewLayer 是 CALayer 的子类，可被用于自动显示相机产生的实时图像。它还有几个工具性质的方法，可将 layer 上的坐标转化到设备上。它看起来像输出，但其实不是。另外，它拥有 session (outputs 被 session 所拥有)。

4.代码实现

  1.初始化AVCaptureSession对象

let session = AVCaptureSession()

  2.现在我们需要一个相机设备输入,我们可以选择后置摄像头或前置摄像头。那么我们必须先遍历所有能提供视频数据的设备(麦克风也属于AVCaptureDevice),并检查position属性:

 let session = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera], mediaType: AVMediaType.video, position: .unspecified)
 let availableCameraDevices = session.devices.compactMap { $0 }
 guard !availableCameraDevices.isEmpty else {throw CameraError.noCamerasAvailable}
 for camera in availableCameraDevices{
         if camera.position == .back {
              backCamera = camera
          }else if camera.position == .front {
                frontCamera = camera
          }
   }

3.获得相关的AVCaptureDeviceInput对象,将它设置为session的输入:

 guard let captureSession = self.captureSession else { throw CameraError.captureSessionIsMissing }
        if let backCamera = self.backCamera {
            self.backCameraInput = try AVCaptureDeviceInput(device:backCamera)
            if(captureSession.canAddInput(self.backCameraInput!)){
                captureSession.addInput(self.backCameraInput!)
            }
            self.currentCameraPosition = .back
        }else if let frontCamera = self.frontCamera{
            self.frontCameraInput = try AVCaptureDeviceInput(device:frontCamera)
            if(captureSession.canAddInput(self.frontCameraInput!)){
                captureSession.addInput(self.frontCameraInput!)
            }
            self.currentCameraPosition = .front
        }else{throw CameraError.noCamerasAvailable}

4.通过AVCapturePhotoOutput配置照片输出:

 guard let captureSession = self.captureSession else { throw CameraError.captureSessionIsMissing }
 self.photoOutput = AVCapturePhotoOutput()
 self.photoOutput!.setPreparedPhotoSettingsArray([AVCapturePhotoSettings(format: [AVVideoCodecKey : AVVideoCodecType.jpeg])], completionHandler: nil)
 if captureSession.canAddOutput(self.photoOutput!) { captureSession.addOutput(self.photoOutput!) }

5.开始运行:

guard let captureSession = self.captureSession else { throw CameraError.captureSessionIsMissing }
captureSession.startRunning()

6.显示来自相机的输出:

 guard let captureSession = self.captureSession, captureSession.isRunning else {
            throw CameraError.captureSessionIsMissing
        }
self.previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
self.previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
self.previewLayer?.connection?.videoOrientation = .landscapeRight
view.layer.insertSublayer(self.previewLayer!, at: 0)
self.previewLayer?.frame = view.frame

7.实现拍照:

let settings = AVCapturePhotoSettings()
settings.flashMode = .off
self.photoOutput?.capturePhoto(with: settings, delegate: self)

8.通过AVCapturePhotoCaptureDelegate获取图片:

func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {
        let imageData = photo.fileDataRepresentation()
}

9.切换摄像头:

 guard let currentCameraPosition = currentCameraPosition, let captureSession = self.captureSession, captureSession.isRunning else { throw CameraError.captureSessionIsMissing }
        
        captureSession.beginConfiguration()
        
        func switchToFrontCamera() throws {
            
            guard let backCameraInput = self.backCameraInput, captureSession.inputs.contains(backCameraInput),
                let frontCamera = self.frontCamera else { throw CameraError.invalidOperation }
            
            self.frontCameraInput = try AVCaptureDeviceInput(device: frontCamera)
            
            captureSession.removeInput(backCameraInput)
            
            if captureSession.canAddInput(self.frontCameraInput!) {
                captureSession.addInput(self.frontCameraInput!)
                
                self.currentCameraPosition = .front
            }
                
            else {
                throw CameraError.invalidOperation
            }
        }
        
        func switchToRearCamera() throws {
            
            guard let frontCameraInput = self.frontCameraInput, captureSession.inputs.contains(frontCameraInput),
                let backCamera = self.backCamera else { throw CameraError.invalidOperation }
            
            self.backCameraInput = try AVCaptureDeviceInput(device: backCamera)
            
            captureSession.removeInput(frontCameraInput)
            
            if captureSession.canAddInput(self.backCameraInput!) {
                captureSession.addInput(self.backCameraInput!)
                
                self.currentCameraPosition = .back
            }
                
            else { throw CameraError.invalidOperation }
        }
        
        switch currentCameraPosition {
        case .front:
            try switchToRearCamera()
        case .back:
            try switchToFrontCamera()
        }
        captureSession.commitConfiguration()
    }

最后需要在info.plist添加访问相机的权限:

camera.png