AVFoundation

一、视频采集(也可以称为捕捉)

AV Foundation 照片和视频捕捉功能是从框架搭建之初就是它的强项。 从iOS 4.0 我们就可以直接访问iOS的摄像头和摄像头生成的数据(照片、视频)。目前捕捉功能仍然是苹果公司多媒体工程师最关注的领域。 核心的捕捉类在iOS 和 OS X上是一致的。除了Mac OSX 为截屏功能定义了AVCaptureScreenInput 类。但iOS上由于沙盒的限制不提供该类。我们讨论的大部分功能都适应于OS X开发的。想尝试Mac开发的同学,可以挑战一下哦!
思维导图:https://zhimap.com/medit/95df35a2c8e44e2c83a8e05d7be37e62

捕捉会话(AVCaptureSession)

AV Foundation 捕捉栈核心类是AVCaptureSession。一个捕捉会话相当于一个虚拟的“插线板”。用于连接输入和输出的资源。

捕捉设备(AVCaptureDevice)

AVCaptureDevice为摄像头、麦克风等物理设备提供接口。大部分我们使用的设备都是内置于MAC或者iPhone、iPad上的。当然也可能出现外部设备。但是AVCaptureDevice 针对物理设备提供了大量的控制方法。比如控制摄像头聚焦、曝光、白平衡、闪光灯等。

捕捉设备的输入(AVCaptureDeviceInput)

注意:为捕捉设备添加输入,不能添加到AVCaptureSession 中,必须通过将它封装到一个AVCaptureDeviceInput实例中。这个对象在设备输入数据和捕捉会话间扮演插头的作用。

捕捉的输出(AVCaptureOutput)

AVCaptureOutput 是一个抽象类。用于为捕捉会话得到的数据寻找输出的目的地。框架定义了一些抽象类的高级扩展类。例如 AVCaptureStillImageOutput 和 AVCaptureMovieFileOutput类。使用它们来捕捉静态照片、视频。例如 AVCaptureAudioDataOutput 和 AVCaptureVideoDataOutput ,使用它们来直接访问硬件捕捉到的数字样本。

捕捉连接(AVCaptureConnection)

AVCaptureConnection类.捕捉会话先确定由给定捕捉设备输入渲染的媒体类型,并自动建立其到能够接收该媒体类型的捕捉输出端的连接。

捕捉预览(AVCaptureVideoPreviewLayer)

如果不能在影像捕捉中看到正在捕捉的场景,那么应用程序用户体验就会很差。幸运的是框架定义了AVCaptureVideoPreviewLayer 类来满足该需求。这样就可以对捕捉的数据进行实时预览。
1.捕捉会话的相关设置

- (BOOL)setupSession:(NSError **)error {

    
    //创建捕捉会话。AVCaptureSession 是捕捉场景的中心枢纽
    self.captureSession = [[AVCaptureSession alloc]init];
    
    /*
     AVCaptureSessionPresetHigh
     AVCaptureSessionPresetMedium
     AVCaptureSessionPresetLow
     AVCaptureSessionPreset640x480
     AVCaptureSessionPreset1280x720
     AVCaptureSessionPresetPhoto
     */
    //设置图像的分辨率
    self.captureSession.sessionPreset = AVCaptureSessionPresetHigh;
    
    //拿到默认视频捕捉设备 iOS系统返回后置摄像头
    AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    
    //将捕捉设备封装成AVCaptureDeviceInput
    //注意:为会话添加捕捉设备,必须将设备封装成AVCaptureDeviceInput对象
    AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:error];
    
    //判断videoInput是否有效
    if (videoInput)
    {
        //canAddInput:测试是否能被添加到会话中
        if ([self.captureSession canAddInput:videoInput])
        {
            //将videoInput 添加到 captureSession中
            [self.captureSession addInput:videoInput];
            self.activeVideoInput = videoInput;
        }else{
            return NO;
        }
    }else
    {
        return NO;
    }
    
    //选择默认音频捕捉设备 即返回一个内置麦克风
    AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    
    //为这个设备创建一个捕捉设备输入
    AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:error];
   
    //判断audioInput是否有效
    if (audioInput) {
        
        //canAddInput:测试是否能被添加到会话中
        if ([self.captureSession canAddInput:audioInput])
        {
            //将audioInput 添加到 captureSession中
            [self.captureSession addInput:audioInput];
        }else{
            return NO;
        }
    }else
    {
        return NO;
    }

    //AVCaptureStillImageOutput 实例 从摄像头捕捉静态图片
    self.imageOutput = [[AVCaptureStillImageOutput alloc]init];
    
    //配置字典:希望捕捉到JPEG格式的图片
    self.imageOutput.outputSettings = @{AVVideoCodecKey:AVVideoCodecJPEG};
    
    //输出连接 判断是否可用,可用则添加到输出连接中去
    if ([self.captureSession canAddOutput:self.imageOutput])
    {
        [self.captureSession addOutput:self.imageOutput];
        
    }
    
    
    //创建一个AVCaptureMovieFileOutput 实例,用于将Quick Time 电影录制到文件系统
    self.movieOutput = [[AVCaptureMovieFileOutput alloc]init];
    
    //输出连接 判断是否可用,可用则添加到输出连接中去
    if ([self.captureSession canAddOutput:self.movieOutput])
    {
        [self.captureSession addOutput:self.movieOutput];
    }
    
    
    self.videoQueue = dispatch_queue_create("videoQueue", NULL);
    
    return YES;
}

2.开始采集

- (void)startSession {

    //检查是否处于运行状态
    if (![self.captureSession isRunning])
    {
        //使用同步调用会损耗一定的时间,则用异步的方式处理
        dispatch_async(self.videoQueue, ^{
            [self.captureSession startRunning];
        });
        
    }
}

3.停止采集

- (void)stopSession {
    
    //检查是否处于运行状态
    if ([self.captureSession isRunning])
    {
        //使用异步方式,停止运行
        dispatch_async(self.videoQueue, ^{
            [self.captureSession stopRunning];
        });
    }
    
}

4.根据摄像头方向找到AVCaptureDevice

- (AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition)position {
    
    //获取可用视频设备
    NSArray *devicess = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    
    //遍历可用的视频设备 并返回position 参数值
    for (AVCaptureDevice *device in devicess)
    {
        if (device.position == position) {
            return device;
        }
    }
    return nil;    
}

5.获取当前捕捉会话对应的摄像头的device

- (AVCaptureDevice *)activeCamera {

    //返回当前捕捉会话对应的摄像头的device 属性
    return self.activeVideoInput.device;
}

6.获取到当前未激活的摄像头

//返回当前未激活的摄像头
- (AVCaptureDevice *)inactiveCamera {

    //通过查找当前激活摄像头的反向摄像头获得,如果设备只有1个摄像头,则返回nil
       AVCaptureDevice *device = nil;
      if (self.cameraCount > 1)
      {
          if ([self activeCamera].position == AVCaptureDevicePositionBack) {
               device = [self cameraWithPosition:AVCaptureDevicePositionFront];
         }else
         {
             device = [self cameraWithPosition:AVCaptureDevicePositionBack];
         }
     }

    return device;
   
}

7.获取视频捕捉设备的数量

//可用视频捕捉设备的数量
- (NSUInteger)cameraCount {

     return [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count];
    
}

8.是否可以切换摄像头

//判断是否有超过1个摄像头可用
- (BOOL)canSwitchCameras {

    
    return self.cameraCount > 1;
}

8.切换摄像头

//切换摄像头
- (BOOL)switchCameras {

    //判断是否有多个摄像头
    if (![self canSwitchCameras])
    {
        return NO;
    }
    
    //获取当前设备的反向设备
    NSError *error;
    AVCaptureDevice *videoDevice = [self inactiveCamera];
    
    
    //将输入设备封装成AVCaptureDeviceInput
    AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    
    //判断videoInput 是否为nil
    if (videoInput)
    {
        //标注原配置变化开始
        [self.captureSession beginConfiguration];
        
        //将捕捉会话中,原本的捕捉输入设备移除
        [self.captureSession removeInput:self.activeVideoInput];
        
        //判断新的设备是否能加入
        if ([self.captureSession canAddInput:videoInput])
        {
            //能加入成功,则将videoInput 作为新的视频捕捉设备
            [self.captureSession addInput:videoInput];
            
            //将获得设备 改为 videoInput
            self.activeVideoInput = videoInput;
        }else
        {
            //如果新设备,无法加入。则将原本的视频捕捉设备重新加入到捕捉会话中
            [self.captureSession addInput:self.activeVideoInput];
        }
        
        //配置完成后, AVCaptureSession commitConfiguration 会分批的将所有变更整合在一起。
        [self.captureSession commitConfiguration];
    }else
    {
        //创建AVCaptureDeviceInput 出现错误,则通知委托来处理该错误
        [self.delegate deviceConfigurationFailedWithError:error];
        return NO;
    }
    
    
    
    return YES;
}

AVCapture Device 定义了很多方法,让开发者控制ios设备上的摄像头。可以独立调整和锁定摄像头的焦距、曝光、白平衡。对焦和曝光可以基于特定的兴趣点进行设置,使其在应用中实现点击对焦、点击曝光的功能。还可以让你控制设备的LED作为拍照的闪光灯或手电筒的使用

每当修改摄像头设备时,一定要先测试修改动作是否能被设备支持。并不是所有的摄像头都支持所有功能,例如前置摄像头就不支持对焦操作,因为它和目标距离一般在一臂之长的距离。但大部分后置摄像头是可以支持全尺寸对焦。尝试应用一个不被支持的动作,会导致异常崩溃。所以修改摄像头设备前,需要判断是否支持
9.当前摄像头是够支持聚焦

- (BOOL)cameraSupportsTapToFocus {
    
    //询问激活中的摄像头是否支持兴趣点对焦
    return [[self activeCamera] isFocusPointOfInterestSupported];
}

10.聚焦

- (void)focusAtPoint:(CGPoint)point {
    
    AVCaptureDevice *device = [self activeCamera];
    
    //是否支持兴趣点对焦 & 是否自动对焦模式
    if (device.isFocusPointOfInterestSupported && [device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
        
        NSError *error;
        //锁定设备准备配置,如果获得了锁
        if ([device lockForConfiguration:&error]) {
            
            //将focusPointOfInterest属性设置CGPoint
            device.focusPointOfInterest = point;
            
            //focusMode 设置为AVCaptureFocusModeAutoFocus
            device.focusMode = AVCaptureFocusModeAutoFocus;
            
            //释放该锁定
            [device unlockForConfiguration];
        }else{
            //错误时,则返回给错误处理代理
            [self.delegate deviceConfigurationFailedWithError:error];
        }
        
    }
    
}

11.是否支持曝光

- (BOOL)cameraSupportsTapToExpose {
    
    //询问设备是否支持对一个兴趣点进行曝光
    return [[self activeCamera] isExposurePointOfInterestSupported];
}

12.曝光

static const NSString *THCameraAdjustingExposureContext;

- (void)exposeAtPoint:(CGPoint)point {

    
    AVCaptureDevice *device = [self activeCamera];
    
    AVCaptureExposureMode exposureMode =AVCaptureExposureModeContinuousAutoExposure;
    
    //判断是否支持 AVCaptureExposureModeContinuousAutoExposure 模式
    if (device.isExposurePointOfInterestSupported && [device isExposureModeSupported:exposureMode]) {
        
        NSError *error;
        
        //锁定设备准备配置
        if ([device lockForConfiguration:&error])
        {
            //配置期望值
            device.exposurePointOfInterest = point;
            device.exposureMode = exposureMode;
            
            //判断设备是否支持锁定曝光的模式。
            if ([device isExposureModeSupported:AVCaptureExposureModeLocked]) {
                
                //支持,则使用kvo确定设备的adjustingExposure属性的状态。
                [device addObserver:self forKeyPath:@"adjustingExposure" options:NSKeyValueObservingOptionNew context:&THCameraAdjustingExposureContext];
                
            }
            
            //释放该锁定
            [device unlockForConfiguration];
            
        }else
        {
            [self.delegate deviceConfigurationFailedWithError:error];
        }
        
        
    }
    
}

- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {

    //判断context(上下文)是否为THCameraAdjustingExposureContext
    if (context == &THCameraAdjustingExposureContext) {
        
        //获取device
        AVCaptureDevice *device = (AVCaptureDevice *)object;
        
        //判断设备是否不再调整曝光等级,确认设备的exposureMode是否可以设置为AVCaptureExposureModeLocked
        if(!device.isAdjustingExposure && [device isExposureModeSupported:AVCaptureExposureModeLocked])
        {
            //移除作为adjustingExposure 的self,就不会得到后续变更的通知
            [object removeObserver:self forKeyPath:@"adjustingExposure" context:&THCameraAdjustingExposureContext];
            
            //异步方式调回主队列,
            dispatch_async(dispatch_get_main_queue(), ^{
                NSError *error;
                if ([device lockForConfiguration:&error]) {
                    
                    //修改exposureMode
                    device.exposureMode = AVCaptureExposureModeLocked;
                    
                    //释放该锁定
                    [device unlockForConfiguration];
                    
                }else
                {
                    [self.delegate deviceConfigurationFailedWithError:error];
                }
            });
            
        }
        
    }else
    {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
    
    
}

13.重新设置对焦&曝光

// 重新设置对焦&曝光
- (void)resetFocusAndExposureModes {

    AVCaptureDevice *device = [self activeCamera];
      
    AVCaptureFocusMode focusMode = AVCaptureFocusModeContinuousAutoFocus;
    
    //获取对焦兴趣点 和 连续自动对焦模式 是否被支持
    BOOL canResetFocus = [device isFocusPointOfInterestSupported]&& [device isFocusModeSupported:focusMode];
    
    AVCaptureExposureMode exposureMode = AVCaptureExposureModeContinuousAutoExposure;
    
    //确认曝光度可以被重设
    BOOL canResetExposure = [device isFocusPointOfInterestSupported] && [device isExposureModeSupported:exposureMode];
    
    //回顾一下,捕捉设备空间左上角(0,0),右下角(1,1) 中心点则(0.5,0.5)
    CGPoint centPoint = CGPointMake(0.5f, 0.5f);
    
    NSError *error;
    
    //锁定设备,准备配置
    if ([device lockForConfiguration:&error]) {
        
        //焦点可设,则修改
        if (canResetFocus) {
            device.focusMode = focusMode;
            device.focusPointOfInterest = centPoint;
        }
        
        //曝光度可设,则设置为期望的曝光模式
        if (canResetExposure) {
            device.exposureMode = exposureMode;
            device.exposurePointOfInterest = centPoint;
            
        }
        
        //释放锁定
        [device unlockForConfiguration];
        
    }else
    {
        [self.delegate deviceConfigurationFailedWithError:error];
    }
     
}

14.是否有闪光灯

//判断是否有闪光灯
- (BOOL)cameraHasFlash {

    return [[self activeCamera] hasFlash];

}

15.获取闪光灯模式

//闪光灯模式
- (AVCaptureFlashMode)flashMode {

    
    return [[self activeCamera] flashMode];
}

16.设置闪光灯模式

//设置闪光灯
- (void)setFlashMode:(AVCaptureFlashMode)flashMode {

    //获取会话
    AVCaptureDevice *device = [self activeCamera];
    
    //判断是否支持闪光灯模式
    if ([device isFlashModeSupported:flashMode]) {
    
        //如果支持,则锁定设备
        NSError *error;
        if ([device lockForConfiguration:&error]) {

            //修改闪光灯模式
            device.flashMode = flashMode;
            //修改完成,解锁释放设备
            [device unlockForConfiguration];
            
        }else
        {
            [self.delegate deviceConfigurationFailedWithError:error];
        }
        
    }

}

17.是否支持手电筒

//是否支持手电筒
- (BOOL)cameraHasTorch {

    return [[self activeCamera] hasTorch];
}

18.获取手电筒模式

//手电筒模式
- (AVCaptureTorchMode)torchMode {

    return [[self activeCamera] torchMode];
}

设置手电筒模式

//设置是否打开手电筒
- (void)setTorchMode:(AVCaptureTorchMode)torchMode {

    
    AVCaptureDevice *device = [self activeCamera];
    
    if ([device isTorchModeSupported:torchMode]) {
        
        NSError *error;
        if ([device lockForConfiguration:&error]) {
            
            device.torchMode = torchMode;
            [device unlockForConfiguration];
        }else
        {
            [self.delegate deviceConfigurationFailedWithError:error];
        }

    }
    
}

19.拍摄静态图片

#pragma mark - Image Capture Methods 拍摄静态图片

/*
    AVCaptureStillImageOutput 是AVCaptureOutput的子类。用于捕捉图片
 */
- (void)captureStillImage {
    
    //获取连接
    AVCaptureConnection *connection = [self.imageOutput connectionWithMediaType:AVMediaTypeVideo];
    
    //程序只支持纵向,但是如果用户横向拍照时,需要调整结果照片的方向
    //判断是否支持设置视频方向
    if (connection.isVideoOrientationSupported) {
        
        //获取方向值
        connection.videoOrientation = [self currentVideoOrientation];
    }
    
    //定义一个handler 块,会返回1个图片的NSData数据
    id handler = ^(CMSampleBufferRef sampleBuffer,NSError *error)
                {
                    if (sampleBuffer != NULL) {
                        NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:sampleBuffer];
                        UIImage *image = [[UIImage alloc]initWithData:imageData];
                        
                        //重点:捕捉图片成功后,将图片传递出去
                        [self writeImageToAssetsLibrary:image];
                    }else
                    {
                        NSLog(@"NULL sampleBuffer:%@",[error localizedDescription]);
                    }
                        
                };
    
    //捕捉静态图片
    [self.imageOutput captureStillImageAsynchronouslyFromConnection:connection completionHandler:handler];
    
    
    
}

//获取方向值
- (AVCaptureVideoOrientation)currentVideoOrientation {
    
    AVCaptureVideoOrientation orientation;
    
    //获取UIDevice 的 orientation
    switch ([UIDevice currentDevice].orientation) {
        case UIDeviceOrientationPortrait:
            orientation = AVCaptureVideoOrientationPortrait;
            break;
        case UIDeviceOrientationLandscapeRight:
            orientation = AVCaptureVideoOrientationLandscapeLeft;
            break;
        case UIDeviceOrientationPortraitUpsideDown:
            orientation = AVCaptureVideoOrientationPortraitUpsideDown;
            break;
        default:
            orientation = AVCaptureVideoOrientationLandscapeRight;
            break;
    }
    
    return orientation;

    return 0;
}


/*
    Assets Library 框架 
    用来让开发者通过代码方式访问iOS photo
    注意:会访问到相册,需要修改plist 权限。否则会导致项目崩溃
 */

- (void)writeImageToAssetsLibrary:(UIImage *)image {

    //创建ALAssetsLibrary  实例
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc]init];
    
    //参数1:图片(参数为CGImageRef 所以image.CGImage)
    //参数2:方向参数 转为NSUInteger
    //参数3:写入成功、失败处理
    [library writeImageToSavedPhotosAlbum:image.CGImage
                             orientation:(NSUInteger)image.imageOrientation
                         completionBlock:^(NSURL *assetURL, NSError *error) {
                             //成功后,发送捕捉图片通知。用于绘制程序的左下角的缩略图
                             if (!error)
                             {
                                 [self postThumbnailNotifification:image];
                             }else
                             {
                                 //失败打印错误信息
                                 id message = [error localizedDescription];
                                 NSLog(@"%@",message);
                             }
                         }];
}

//发送缩略图通知
- (void)postThumbnailNotifification:(UIImage *)image {
    
    //回到主队列
    dispatch_async(dispatch_get_main_queue(), ^{
        //发送请求
        NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
        [nc postNotificationName:THThumbnailCreatedNotification object:image];
    });
}

20.拍视频

#pragma mark - Video Capture Methods 捕捉视频

//判断是否录制状态
- (BOOL)isRecording {

    return self.movieOutput.isRecording;
}

//开始录制
- (void)startRecording {

    if (![self isRecording]) {
        
        //获取当前视频捕捉连接信息,用于捕捉视频数据配置一些核心属性
        AVCaptureConnection * videoConnection = [self.movieOutput connectionWithMediaType:AVMediaTypeVideo];
        
        //判断是否支持设置videoOrientation 属性。
        if([videoConnection isVideoOrientationSupported])
        {
            //支持则修改当前视频的方向
            videoConnection.videoOrientation = [self currentVideoOrientation];
            
        }
        
        //判断是否支持视频稳定 可以显著提高视频的质量。只会在录制视频文件涉及
        if([videoConnection isVideoStabilizationSupported])
        {
            videoConnection.enablesVideoStabilizationWhenAvailable = YES;
        }
        
        
        AVCaptureDevice *device = [self activeCamera];
        
        //摄像头可以进行平滑对焦模式操作。即减慢摄像头镜头对焦速度。当用户移动拍摄时摄像头会尝试快速自动对焦。
        if (device.isSmoothAutoFocusEnabled) {
            NSError *error;
            if ([device lockForConfiguration:&error]) {
                
                device.smoothAutoFocusEnabled = YES;
                [device unlockForConfiguration];
            }else
            {
                [self.delegate deviceConfigurationFailedWithError:error];
            }
        }
        
        //查找写入捕捉视频的唯一文件系统URL.
        self.outputURL = [self uniqueURL];
        
        //在捕捉输出上调用方法 参数1:录制保存路径  参数2:代理
        [self.movieOutput startRecordingToOutputFileURL:self.outputURL recordingDelegate:self];
        
    }
    
    
}

- (CMTime)recordedDuration {
    
    return self.movieOutput.recordedDuration;
}


//写入视频唯一文件系统URL
- (NSURL *)uniqueURL {

    NSFileManager *fileManager = [NSFileManager defaultManager];
    
    //temporaryDirectoryWithTemplateString  可以将文件写入的目的创建一个唯一命名的目录;
    NSString *dirPath = [fileManager temporaryDirectoryWithTemplateString:@"camera.XXXXXX"];
    
    if (dirPath) {
        
        NSString *filePath = [dirPath stringByAppendingPathComponent:@"camera_movie.mov"];
        return  [NSURL fileURLWithPath:filePath];
        
    }
    
    return nil;
    
}

//停止录制
- (void)stopRecording {

    //是否正在录制
    if ([self isRecording]) {
        [self.movieOutput stopRecording];
    }
}

21.视频的代理方法

#pragma mark - AVCaptureFileOutputRecordingDelegate

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput
didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL
      fromConnections:(NSArray *)connections
                error:(NSError *)error {

    //错误
    if (error) {
        [self.delegate mediaCaptureFailedWithError:error];
    }else
    {
        //写入
        [self writeVideoToAssetsLibrary:[self.outputURL copy]];
        
    }
    
    self.outputURL = nil;
    

}

//写入捕捉到的视频
- (void)writeVideoToAssetsLibrary:(NSURL *)videoURL {
    
    //ALAssetsLibrary 实例 提供写入视频的接口
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc]init];
    
    //写资源库写入前,检查视频是否可被写入 (写入前尽量养成判断的习惯)
    if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:videoURL]) {
        
        //创建block块
        ALAssetsLibraryWriteVideoCompletionBlock completionBlock;
        completionBlock = ^(NSURL *assetURL,NSError *error)
        {
            if (error) {
                
                [self.delegate assetLibraryWriteFailedWithError:error];
            }else
            {
                //用于界面展示视频缩略图
                [self generateThumbnailForVideoAtURL:videoURL];
            }
            
        };
        
        //执行实际写入资源库的动作
        [library writeVideoAtPathToSavedPhotosAlbum:videoURL completionBlock:completionBlock];
    }
}

//获取视频左下角缩略图
- (void)generateThumbnailForVideoAtURL:(NSURL *)videoURL {

    //在videoQueue 上,
    dispatch_async(self.videoQueue, ^{
        
        //建立新的AVAsset & AVAssetImageGenerator
        AVAsset *asset = [AVAsset assetWithURL:videoURL];
        
        AVAssetImageGenerator *imageGenerator = [AVAssetImageGenerator assetImageGeneratorWithAsset:asset];
        
        //设置maximumSize 宽为100,高为0 根据视频的宽高比来计算图片的高度
        imageGenerator.maximumSize = CGSizeMake(100.0f, 0.0f);
        
        //捕捉视频缩略图会考虑视频的变化(如视频的方向变化),如果不设置,缩略图的方向可能出错
        imageGenerator.appliesPreferredTrackTransform = YES;
        
        //获取CGImageRef图片 注意需要自己管理它的创建和释放
        CGImageRef imageRef = [imageGenerator copyCGImageAtTime:kCMTimeZero actualTime:NULL error:nil];
        
        //将图片转化为UIImage
        UIImage *image = [UIImage imageWithCGImage:imageRef];
        
        //释放CGImageRef imageRef 防止内存泄漏
        CGImageRelease(imageRef);
        
        //回到主线程
        dispatch_async(dispatch_get_main_queue(), ^{
            
            //发送通知,传递最新的image
            [self postThumbnailNotifification:image];
            
        });
        
    });
    
}

二、二维码扫描

AVFoundation扫描二维码:https://www.jianshu.com/p/c15010d58476
用Zabar扫描二维码:https://www.jianshu.com/p/5094d7963ac4

三、AVAudioRecorder录音

https://www.jianshu.com/p/fb0b351f08bb

四、音频的播放

https://www.jianshu.com/p/fd4490cbcd22
https://www.jianshu.com/p/8a003096e328

五、视频的播放

https://www.jianshu.com/p/d38dc83e3a83

六、人脸识别

- (BOOL)setupSessionOutputs:(NSError **)error {

    
    self.metadataOutput = [[AVCaptureMetadataOutput alloc]init];
    
   
    
    //为捕捉会话添加设备
    if ([self.captureSession canAddOutput:self.metadataOutput]){
        [self.captureSession addOutput:self.metadataOutput];
        
        
        //获得人脸属性
        NSArray *metadatObjectTypes = @[AVMetadataObjectTypeFace];
        
        //设置metadataObjectTypes 指定对象输出的元数据类型。
        /*
         限制检查到元数据类型集合的做法是一种优化处理方法。可以减少我们实际感兴趣的对象数量
         支持多种元数据。这里只保留对人脸元数据感兴趣
         */
        self.metadataOutput.metadataObjectTypes = metadatObjectTypes;
        
        //创建主队列: 因为人脸检测用到了硬件加速,而且许多重要的任务都在主线程中执行,所以需要为这次参数指定主队列。
        dispatch_queue_t mainQueue = dispatch_get_main_queue();
        
        
        //通过设置AVCaptureVideoDataOutput的代理,就能获取捕获到一帧一帧数据
        [self.metadataOutput setMetadataObjectsDelegate:self queue:mainQueue];
     
        return YES;
    }else
    {
        //报错
        if (error) {
            NSDictionary *userInfo = @{NSLocalizedDescriptionKey:@"Failed to still image output"};
            
            *error = [NSError errorWithDomain:THCameraErrorDomain code:THCameraErrorFailedToAddOutput userInfo:userInfo];
            
        }
        return NO;
    }

}

#pragma mark - AVCaptureMetadataOutputObjectsDelegate

//捕捉数据
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputMetadataObjects:(NSArray *)metadataObjects
       fromConnection:(AVCaptureConnection *)connection {

    
    //使用循环,打印人脸数据
    for (AVMetadataFaceObject *face in metadataObjects) {
        
        NSLog(@"Face detected with ID:%li",(long)face.faceID);
        NSLog(@"Face bounds:%@",NSStringFromCGRect(face.bounds));
        
    }
    
    
    //将元数据 传递给 THPreviewView.m   将元数据转换为layer
    [self.faceDetectionDelegate didDetectFaces:metadataObjects];
    
}

七、三种代理总结

1.二维码扫描、人脸识别
AVCaptureMetadataOutputObjectsDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{}

2.录制视频(包括视频和音频)

 AVCaptureFileOutputRecordingDelegate
- (void)captureOutput:(AVCaptureFileOutput *)captureOutput
didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL
      fromConnections:(NSArray *)connections
                error:(NSError *)error{}

3.录制视频(仅包括视频,编码时)

AVCaptureVideoDataOutputSampleBufferDelegate
-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{}