利用AVCaptureSession实现拍照与录像功能

### 利用 AVCaptureSession 实现拍照与录像功能 在开发涉及相机功能的应用时，`AVCaptureSession` 是一个强大的工具，它可以帮助我们实现拍照和录像等功能。下面将详细介绍如何使用 `AVCaptureSession` 实现这些功能。 #### 1. 利用 AVCaptureSession 拍摄静态图像 在之前的基础上，我们要扩展项目，实现拍摄静态图像并保存到设备相册的功能。 ##### 1.1 项目准备 - **添加框架**：在项目中添加 `AssetsLibrary.framework`，该框架用于将照片写入相册。 - **添加权限描述**：在应用的 `Info.plist` 文件中添加 `NSPhotoLibraryUsageDescription` 键，并简要说明应用访问相册的原因，例如 “Testing AVCaptureSession”。 ##### 1.2 添加拍摄按钮 - 在视图控制器的故事板视图中添加一个标题为 “Capture” 的按钮，并为该按钮创建一个名为 “capture” 的动作。 - 为确保按钮随屏幕大小调整，选择按钮，从故事板编辑器屏幕右下角的 “Resolve Auto Layout Issues” 菜单中选择 “Add Missing Constraints”。 ##### 1.3 修改代码 - **ViewController.h 文件**：导入 `AssetsLibrary` 框架，并添加一个属性来保存静态图像输出实例。 ```objc // // ViewController.h // Recipe 9-6: Taking Still Images With AVCaptureSession // #import <UIKit/UIKit.h> #import <AVFoundation/AVFoundation.h> #import <AssetsLibrary/AssetsLibrary.h> @interface ViewController : UIViewController @property (strong, nonatomic) AVCaptureSession *captureSession; @property (strong, nonatomic) AVCaptureDeviceInput *videoInput; @property (strong, nonatomic) AVCaptureStillImageOutput *stillImageOutput; - (IBAction)capture:(id)sender; @end ``` - **ViewController.m 文件**：在 `viewDidLoad` 方法中添加代码，分配并初始化静态图像输出对象，并将其连接到捕获会话。 ```objc - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. self.captureSession = [[AVCaptureSession alloc] init]; //Optional: self.captureSession.sessionPreset = AVCaptureSessionPresetMedium; AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; NSError *error = nil; self.videoInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error]; if (self.videoInput) { [self.captureSession addInput:self.videoInput]; } else { NSLog(@"Input Error: %@", error); } self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init]; NSDictionary *stillImageOutputSettings = [[NSDictionary alloc] initWithObjectsAndKeys: AVVideoCodecJPEG, AVVideoCodecKey, nil]; [self.stillImageOutput setOutputSettings:stillImageOutputSettings]; [self.captureSession addOutput:self.stillImageOutput]; AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession]; UIView *aView = self.view; previewLayer.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height-70); [aView.layer addSublayer:previewLayer]; } ``` ##### 1.4 实现拍摄方法 - **`capture` 动作方法**：调用 `captureStillImage` 方法。 ```objc - (IBAction)capture:(id)sender { [self captureStillImage]; } ``` - **`captureStillImage` 方法**： ```objc - (void) captureStillImage { AVCaptureConnection *stillImageConnection = [self.stillImageOutput.connections objectAtIndex:0]; if ([stillImageConnection isVideoOrientationSupported]) [stillImageConnection setVideoOrientation:AVCaptureVideoOrientationPortrait]; [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:stillImageConnection completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) { if (imageDataSampleBuffer != NULL) { NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer]; ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init]; UIImage *image = [[UIImage alloc] initWithData:imageData]; [library writeImageToSavedPhotosAlbum:[image CGImage] orientation:(ALAssetOrientation)[image imageOrientation] completionBlock:^(NSURL *assetURL, NSError *error) { UIAlertView *alert; if (!error) { alert = [[UIAlertView alloc] initWithTitle:@"Photo Saved" message:@"The photo was successfully saved to your photos library" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil]; } else { alert = [[UIAlertView alloc] initWithTitle:@"Error Saving Photo" message:@"The photo was not saved to your photos library" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil]; } [alert show]; } ]; } else { NSLog(@"Error capturing still image: %@", error); } } ]; } ``` #### 2. 利用 AVCaptureSession 录制视频 接下来，我们要扩展应用，实现录制视频的功能，并允许用户在拍照和录像模式之间切换。 ##### 2.1 添加视频录制模式 - 在用户界面中添加一个分段控件，将两个分段的默认文本改为 “Take Photo” 和 “Record Video”，使视图类似于图 9 - 13。 - 为分段控件和按钮添加输出口，分别命名为 “modeControl” 和 “captureButton”，并为分段控件的值变化事件创建一个名为 “updateMode” 的动作。 ##### 2.2 修改代码 - **ViewController.h 文件**：添加音频输入和电影文件输出的属性，并实现 `AVCaptureFileOutputRecordingDelegate` 协议。 ```objc // // ViewController.h // Recipe 9-7 Recording Video With AVCaptureSession // #import <UIKit/UIKit.h> #import <AVFoundation/AVFoundation.h> #import <AssetsLibrary/AssetsLibrary.h> @interface ViewController : UIViewController <AVCaptureFileOutputRecordingDelegate> @property (strong, nonatomic) AVCaptureSession *captureSession; @property (strong, nonatomic) AVCaptureDeviceInput *videoInput; @property (strong, nonatomic) AVCaptureDeviceInput *audioInput; @property (strong, nonatomic) AVCaptureStillImageOutput *stillImageOutput; @property (strong, nonatomic) AVCaptureMovieFileOutput *movieOutput; @property (weak, nonatomic) IBOutlet UIButton *captureButton; @property (weak, nonatomic) IBOutlet UISegmentedControl *modeControl; - (IBAction)capture:(id)sender; - (IBAction)updateMode:(id)sender; @end ``` - **ViewController.m 文件**： - **`viewDidLoad` 方法**：设置音频输入对象、电影文件输出对象，并调整预览层的大小。 ```objc - (void)viewDidLoad { [super viewDidLoad]; self.captureSession = [[AVCaptureSession alloc] init]; //Optional: self.captureSession.sessionPreset = AVCaptureSessionPresetMedium; AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio]; NSError *error = nil; self.videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error]; self.audioInput = [[AVCaptureDeviceInput alloc] initWithDevice:audioDevice error:&error]; if (self.videoInput) { self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init]; NSDictionary *stillImageOutputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG, AVVideoCodecKey, nil]; [self.stillImageOutput setOutputSettings:stillImageOutputSettings]; self.movieOutput = [[AVCaptureMovieFileOutpu ```