iOS开发：相机与多媒体功能实现指南

### iOS开发：相机与多媒体功能实现指南 #### 1. 相机视频录制 在iOS开发中，使用AVFoundation框架可以实现强大的相机和音频功能。下面将详细介绍如何实现视频录制功能。 ##### 1.1 创建项目 首先，创建一个名为“Chapter6Recipe6”的新项目，类前缀为“CustomVideo”。 ##### 1.2 引入必要的框架 在项目的Build Phases标签的Link Binary With Libraries部分添加以下框架： - AV Foundation：用于处理相机和麦克风。 - Assets Library：用于将录制的视频保存到设备中。 ##### 1.3 界面设置 在Interface Builder中，在视图控制器的视图底部中心添加一个UIButton，默认标签为“Record”。将其连接到头文件，命名为“button”，并创建一个名为`-recordPressed:`的动作。 ##### 1.4 头文件设置 在视图控制器的头文件中添加以下内容： ```objc #import <UIKit/UIKit.h> #import <AVFoundation/AVFoundation.h> #import <AssetsLibrary/AssetsLibrary.h> @interface CustomVideoViewController : UIViewController <AVCaptureFileOutputRecordingDelegate>{ UIButton *button; BOOL recording; } @property (strong, nonatomic) IBOutlet UIButton *button; @property (strong, nonatomic) AVCaptureSession *session; @property (strong, nonatomic) AVCaptureMovieFileOutput *output; -(IBAction)recordPressed:(id)sender; @end ``` ##### 1.5 实现文件设置 在实现文件中，需要合成`session`和`output`属性，并在`-viewDidUnload`方法中将它们设置为`nil`。 `-viewDidLoad`方法的实现如下： ```objc - (void)viewDidLoad { [super viewDidLoad]; self.session = [[AVCaptureSession alloc] init]; self.session.sessionPreset = AVCaptureSessionPresetMedium; AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; NSError *error = nil; AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error]; NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeAudio]; AVCaptureDeviceInput *mic = [[AVCaptureDeviceInput alloc] initWithDevice:[devices objectAtIndex:0] error:nil]; if (!input || !mic) { NSLog(@"Input Error"); } else { [self.session addInput:input]; [self.session addInput:mic]; } self.output = [[AVCaptureMovieFileOutput alloc] init]; NSArray *connections = self.output.connections; for (AVCaptureConnection *connection in connections) { if ([connection isVideoOrientationSupported]) connection.videoOrientation = AVCaptureVideoOrientationPortrait; } if ([self.session canAddOutput:self.output]) [self.session addOutput:self.output]; AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.session]; UIView *aView = self.view; previewLayer.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height-70); [aView.layer addSublayer:previewLayer]; [self.session startRunning]; recording = NO; } ``` ##### 1.6 录制控制 实现`-recordPressed:`方法，用于控制录制的开始和停止： ```objc -(IBAction)recordPressed:(id)sender { if (!recording) { [self.button setTitle:@"Stop" forState:UIControlStateNormal]; recording = YES; NSURL *fileURL = [self tempFileURL]; [self.output startRecordingToOutputFileURL:fileURL recordingDelegate:self]; } else { [self.button setTitle:@"Record" forState:UIControlStateNormal]; [self.output stopRecording]; recording = NO; } } ``` ##### 1.7 临时文件路径 实现`-tempFileURL`方法，用于返回录制视频的临时保存路径： ```objc - (NSURL *) tempFileURL { NSString *outputPath = [[NSString alloc] initWithFormat:@"%@%@", NSTemporaryDirectory(), @"output.mov"]; NSURL *outputURL = [[NSURL alloc] initFileURLWithPath:outputPath]; NSFileManager *manager = [[NSFileManager alloc] init]; if ([manager fileExistsAtPath:outputPath]) { [manager removeItemAtPath:outputPath error:nil]; } return outputURL; } ``` ##### 1.8 录制完成处理 实现`-captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error:`方法，用于检查录制是否成功，并将视频保存到Asset Library： ```objc - (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error { BOOL recordedSuccessfully = YES; if ([error code] != noErr) { id value = [[error userInfo] objectForKey:AVErrorRecordingSuccessfullyFinishedKey]; if (value) { recordedSuccessfully = [value boolValue]; } } ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init]; [library writeVideoAtPathToSavedPhotosAlbum:outputFileURL completionBlock:^(NSURL *assetURL, NSError *error) { if (error) { NSLog(@"Error writing") ; } }]; } ``` ##### 1.9 优化功能 实现`-viewWillAppear:`和`-viewWillDisappear:`方法，用于控制会话的启动和停止： ```objc - (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; if (![self.session isRunning]) { [self.session startRunning]; } } - (void)viewWillDisappear:(BOOL)animated { [super viewWillDisappear:animated]; if ([self.session isRunning]) { [self.session stopRunning]; } } ``` #### 2. 视频帧捕获 在视频应用中，缩略图图像常用于代表视频。下面将介绍两种从视频中捕获缩略图的方法。 ##### 2.1 界面设置 在视图控制器的XIB文件中添加两个`UIImageView`，连接到头文件，命名为`imageViewThumb`和`imageViewThumb2`。 ##### 2.2 头文件设置 在视图控制器中声明并合成`stillImageOutput`属性，并在`-viewDidUnload`方法中将其设置为`nil`。 ##### 2.3 `-viewDidLoad`方法更新 在`-viewDidLoad`方法中添加`AVCaptureStillImageOutput`： ```objc - (void)viewDidLoad { [super viewDidLoad]; self.imageViewThumb.backgroundColor = [UIColor whiteColor]; self.session = [[AVCaptureSession alloc] init]; self.session.sessionPreset = AVCaptureSessionPresetMedium; AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; NSError *error = nil; AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error]; NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeAudio]; AVCaptureD ```