AVFoundationAVFoundation 主要是用于多媒体信息的采集。 1. 基本概念 2. 回调处理 3. 控

AVFoundation 主要是用于多媒体信息的采集。

用途：照片采集和音、视频采集
应用：相机，小视频，直播

1. 基本概念

捕捉会话：AVCaptureSession, 需要配置采集的分辨率 sessionPreset
捕捉设备：AVCaptureDevice（前、后摄像头，麦克风）
- 获取视频捕捉设备 [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]
- 获取音频捕捉设备 [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio]

捕捉设备的输入：AVCaptureDeviceInput (音频输入，视频输入)，注意在添加输入设备的时候需要做一下判断

AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:error];
if ([self.captureSession canAddInput:videoInput])
{
    //将videoInput 添加到 captureSession中
    [self.captureSession addInput:videoInput]; 
}

捕捉设备输出：AVCaptureOutput (抽象基类)，在添加输出设备的时候需要做一下判断 - (BOOL)canAddOutput:(AVCaptureOutput *)output;
- AVCaptureStillImageOutput：输出静态图片
- AVCaptureMovieFileOutput：输出视频文件（格式为 MOV）
- AVCaptureAudioDataOutput: 输出音频数据
- AVCaptureVideoDataOutput: 输出视频数据
捕捉连接：AVCaptureConnection （建立输入输出的连接）
- 音频连接： [self.audioDataOutput connectionWithMediaType:AVMediaTypeAudio]
- 视频连接： [self.videoDataOutput connectionWithMediaType:AVMediaTypeVideo]
捕捉预览：AVCaptureVideoPreviewLayer (预览图层)

2. 回调处理

2.1 音频数据 & 视频数据

实现 AVCaptureAudioDataOutputSampleBufferDelegate 和 AVCaptureVideoDataOutputSampleBufferDelegate 的代理方法：

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    /*
     在这里可以根据 captureOutput 来判断媒体类型, 也可以根据 connection 来判断
     */
    if (connection == self.audioConnection) {
        if (self.delegate && [self.delegate respondsToSelector:@selector(didCaptureSampleBuffer:type:)]) {
            [self.delegate didCaptureSampleBuffer:sampleBuffer type:YYCaptureTypeAudio];
        }
    } else if (connection == self.videoConnection) {
        if (self.delegate && [self.delegate respondsToSelector:@selector(didCaptureSampleBuffer:type:)]) {
            [self.delegate didCaptureSampleBuffer:sampleBuffer type:YYCaptureTypeVideo];
        }
    }
}

2.2 捕获静态图片（拍照）

AVCaptureConnection *connection = [self.imageOutput connectionWithMediaType:AVMediaTypeVideo];
[self.imageOutput captureStillImageAsynchronouslyFromConnection:connection completionHandler:^(CMSampleBufferRef  _Nullable imageDataSampleBuffer, NSError * _Nullable error) {
    
    if (imageDataSampleBuffer) {
        // 获取图片数据
        NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
        // 生成 UIImage
        UIImage *image = [[UIImage alloc]initWithData:imageData];
    }
}];

2.3 视频文件录制

实现 AVCaptureFileOutputRecordingDelegate 的代理方法：

-(void)captureOutput:(AVCaptureFileOutput *)captureOutput didStartRecordingToOutputFileAtURL:(NSURL *)fileURL fromConnections:(NSArray *)connections
{
    // 开始录制... 
}

-(void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error
{
    // 视频录制完成... 
}

3. 控制

3.1 摄像头

是否支持切换摄像头，如果摄像头个数大于 1 就支持

- (BOOL)canSwitchCameras {
    return [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count] > 1;
}

切换摄像头，获取当前不在使用的摄像头，如果是前置摄像头就返回后置，反之亦然，然后修改 session 配置。

// 返回当前未使用的摄像头
- (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; 
}
//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;
}

3.2 聚焦

是否支持聚焦

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

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];
        } 
    } 
}

3.3 曝光

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];
}

修改曝光设置

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]) { 
        [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];
                }
            }); 
        } 
    } 
}

3.4 闪光灯

判断是否有闪光灯

//判断是否有闪光灯
- (BOOL)cameraHasFlash {
    return [[self activeCamera]hasFlash];
}

获取当前闪光灯模式

//闪光灯模式
- (AVCaptureFlashMode)flashMode { 
    return [[self activeCamera] flashMode];
}

设置闪光灯模式

- (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];
        } 
    } 
}

3.5 手电筒

是否支持手电筒

- (BOOL)cameraHasTorch {
    return [[self activeCamera]hasTorch];
}

获取当前手电筒模式

- (AVCaptureTorchMode)torchMode {
    return [[self activeCamera]torchMode];
}

修改手电筒模式

- (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];
        } 
    } 
}

4. 其他

4.1 给录制的视频生成缩略图

- (void)createThumbnailImageForVideoWithURL:(NSURL *)videoURL {
    //在 videoQueue 上生成图片
    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);
        
        dispatch_async(dispatch_get_main_queue(), ^{
            
            // 回到主线程使用最新生成的image... 
        }); 
    }); 
}

4.2 不同的坐标系 CGPoint 转换

- (CGPoint)captureDevicePointFromScreenPoint:(CGPoint)point {
    /**
     AVCaptureVideoPreviewLayer 定义了两个坐标系 CGPoint 的转换方法:
     captureDevicePointOfInterestForPoint: 根据屏幕坐标系的 CGPoint 转为摄像头坐标系的 CGPoint
     layer pointForCaptureDevicePointOfInterest: 根据摄像头坐标系的 CGPoint 转为屏幕坐标系的 CGPoint
     */
    AVCaptureVideoPreviewLayer *layer = (AVCaptureVideoPreviewLayer*)self.layer;
    return [layer captureDevicePointOfInterestForPoint:point];
}