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:
