AVFoundation框架(五) 媒体捕捉上- 简单的录制

2017-03-01 本文已影响158人 ValienZh

1. 媒体捕捉的类

AVFoundation的照片和视频捕捉功能是它的强项.先看一下其中捕捉相关的类.

找到唯一比较清楚的图.png

捕捉会话 AVCaptureSession:
AVCaptureSession相当于一个虚拟的插座,连接了输入和输出资源.它管理着从物理设备(摄像头和麦克风)得到的数据流,然后输出到其他地方.
可以额外配置一个会话预设值,用来控制捕捉数据的格式和质量,默认是AVCaptureSessionPresetHigh。
捕捉设备 AVCaptureDevice:
AVCaptureDevice为物理设备定义一个接口和大量控制方法,例如对焦、曝光、白平衡和闪光等。
捕捉设备输入 AVCaptureDeviceInput:
在使用AVCaptureDevice进行处理前,需要将它封装到AVCaptureDeviceInput实例中.因为一个捕捉设备不能直接添加到AVCaptureSession中; 如下:

NSError *error;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];

捕捉的输出 AVCaptureOutput:
AVCaptureOutput有许多扩展类,它本身只是一个抽象基类,用于为从Session得到的数据寻找输出目的地. 看上面结构图就可以看出各扩展类功能方向, 这里单独说一下, AVCaptureAudioDataOutput和AVCaptureVideoDataOutput可以直接访问硬件扑捉到的数字样本,可以用于音视频流进行实施处理.
捕捉连接 AVCaptureConnection
这个类其实就是上图中连接不同组件的连接箭头所表示. 对这些连接的访问可以让开发者对信号流就行底层控制,比如禁用某些特定的连接,或者音频连接中限制单独的音频轨道.
捕捉预览 AVCaptureVideoPreviewLayer
这个类不在上图中, 它是对捕捉视频数据进行实时预览.在视频角色中类似于AVPlayerLayer

捕捉会话应用流程:

第一步:配置会话

- (BOOL)setupSession:(NSError **)error {
    // 1. 创建捕捉会话
    self.captureSession = [[AVCaptureSession alloc] init];                  
    self.captureSession.sessionPreset = AVCaptureSessionPresetHigh;

     //2. 根据要生成的媒体类型获取捕捉设备,并添加到Session上.
    AVCaptureDevice *videoDevice =                                          
        [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
           // 在把此捕捉设备添加到AVCaptureSession之前,先封装成一个input对象.
    AVCaptureDeviceInput *videoInput =                                      
        [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:error];
    if (videoInput) {
        if ([self.captureSession canAddInput:videoInput]) {  // 测试是否可以add
            [self.captureSession addInput:videoInput];
            self.activeVideoInput = videoInput;
        }
    } else {
        return NO;
    }
/*// 如果要获取音频捕捉部分
    AVCaptureDevice *audioDevice =                                          
        [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    AVCaptureDeviceInput *audioInput =                                      
        [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:error];
    if (audioInput) {
        if ([self.captureSession canAddInput:audioInput]) {                
            [self.captureSession addInput:audioInput];
        }
    } else {
        return NO;
    }
*/

     //3. 设置捕捉会话的输出部分
        // image输出
    self.imageOutput = [[AVCaptureStillImageOutput alloc] init];            
    self.imageOutput.outputSettings = @{AVVideoCodecKey : AVVideoCodecJPEG};

    if ([self.captureSession canAddOutput:self.imageOutput]) {
        [self.captureSession addOutput:self.imageOutput];
    }

      // movie输出
    self.movieOutput = [[AVCaptureMovieFileOutput alloc] init];             

    if ([self.captureSession canAddOutput:self.movieOutput]) {
        [self.captureSession addOutput:self.movieOutput];
    }

    return YES;
}

第二: 启动和停止会话

- (void)startSession {
    if (![self.captureSession isRunning]) {                                 
        dispatch_async([self globalQueue], ^{
            [self.captureSession startRunning];
        });
    }
}

- (void)stopSession {
    if ([self.captureSession isRunning]) {                                  
        dispatch_async([self globalQueue], ^{
            [self.captureSession stopRunning];
        });
    }
}
// 开始和停止会话都是同步耗时操作,所以采用异步执行.
- (dispatch_queue_t)globalQueue {
    return dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
}

iOS 8之后使用硬件设备都需要用户给予权限,使用前都要判断下. 例如:

AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
    if(authStatus == AVAuthorizationStatusRestricted || authStatus == AVAuthorizationStatusDenied) {
  NSLog(@"相机权限受限!");
}

2. 细节部分.

2.1 捕捉设备的修改与配置

获取摄像头,切换摄像头.

// 当前捕捉会话对应的摄像头.
- (AVCaptureDevice *)activeCamera {                                         
    return self.activeVideoInput.device;
}
// 当前未激活的摄像头 
- (AVCaptureDevice *)inactiveCamera {                                      
    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 {

    if (![self canSwitchCameras]) {                                         
        return NO;
    }

    // 1. 获取当前未使用的摄像头,并为他创建一个新的Input.
    NSError *error;
    AVCaptureDevice *videoDevice = [self inactiveCamera];                   
    AVCaptureDeviceInput *videoInput =
    [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    // 2. 用新的Input替换掉正在激活的Input
    if (videoInput) {
        [self.captureSession beginConfiguration];    // 原子性配置开始.保证线程安全

        [self.captureSession removeInput:self.activeVideoInput];            

        if ([self.captureSession canAddInput:videoInput]) {                 
            [self.captureSession addInput:videoInput];
            self.activeVideoInput = videoInput;
        } else { // 确保安全,如果新的Input不能添加,继续使用旧的
            [self.captureSession addInput:self.activeVideoInput];
        }

        [self.captureSession commitConfiguration];    // 原子性配置完成

    } else {    // 错误处理
        [self.delegate deviceConfigurationFailedWithError:error];           
        return NO;
    }

    return YES;
}

- (BOOL)canSwitchCameras {                                                  
    return self.cameraCount > 1;
}

- (NSUInteger)cameraCount {                                                 
    return [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count];
}

// 获取指定位置的AVCaptureDevice
- (AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition)position { 
    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    for (AVCaptureDevice *device in devices) {  
        if (device.position == position) {
            return device;
        }
    }
    return nil;
}

调整焦距和曝光
修改AVCaptureDevice配置设备时,一定要先测试修改动作是否被硬件设备支持. 比如前置摄像头不支持对焦操作.尝试一个不被支持的修改动作就会导致程序崩溃. 所以任何修改都要先通过判断一下.

/* 调整对焦 */
- (void)focusAtPoint:(CGPoint)point {                                      
    AVCaptureDevice *device = self.activeVideoInput.device;

    if (device.isFocusPointOfInterestSupported &&                          
        [device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {     // 判断设备是否支持兴趣点对焦和自动对焦模式.

        NSError *error;
        if ([device lockForConfiguration:&error]) {    // 锁定设备,准备配置修改. 之后修改完释放锁定.
            device.focusPointOfInterest = point;
            device.focusMode = AVCaptureFocusModeAutoFocus;

            [device unlockForConfiguration];
        } else {
            [self.delegate deviceConfigurationFailedWithError:error];
        }
    }
}


/* 
调整曝光 
曝光模式定义了四种方式: 
    AVCaptureExposureModeLocked                            锁定
    AVCaptureExposureModeAutoExpose                    调整一次并锁定
    AVCaptureExposureModeContinuousAutoExposure            一直自动调整
    AVCaptureExposureModeCustom                 
大部分设备是根据环境自动调整, 现在我们做调整曝光度并锁定.  但在iOS中并不支持AVCaptureExposureModeAutoExpose, 所以我们要用其他定义来实现.这个功能
*/
static const NSString *THCameraAdjustingExposureContext;
- (void)exposeAtPoint:(CGPoint)point {

    AVCaptureDevice *device = self.activeVideoInput.device;

    AVCaptureExposureMode exposureMode =
    AVCaptureExposureModeContinuousAutoExposure;

    if (device.isExposurePointOfInterestSupported &&
        [device isExposureModeSupported:exposureMode]) {    // 判断设备是否支持AutoExposure模式

        NSError *error;
        if ([device lockForConfiguration:&error]) {    // 锁定设备,准备配置修改. 之后修改完释放锁定.

            device.exposurePointOfInterest = point;
            device.exposureMode = exposureMode;

            // 判断设备是否支持锁定曝光设置, 如果支持,使用KVO来观察设备"adjustingExposure"属性状态. 然后在曝光调整完成时在该点上锁定曝光.
            if ([device isExposureModeSupported:AVCaptureExposureModeLocked]) {
                [device addObserver:self                                    
                         forKeyPath:@"adjustingExposure"
                            options:NSKeyValueObservingOptionNew
                            context:&THCameraAdjustingExposureContext];
            }

            [device unlockForConfiguration];
        } else {
            [self.delegate deviceConfigurationFailedWithError:error];
        }
    }
}

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

    if (context == &THCameraAdjustingExposureContext) {    
    // 这里通过测试Context是否为&THCameraAdjustingExposureContext指针,来判断监听到的回调是否对应我们期望的变更操作.

        AVCaptureDevice *device = (AVCaptureDevice *)object;
        if (!device.isAdjustingExposure &&                                  
            [device isExposureModeSupported:AVCaptureExposureModeLocked]) {

            [object removeObserver:self                                     
                        forKeyPath:@"adjustingExposure"
                           context:&THCameraAdjustingExposureContext];
            // 回到主队列设置exposureMode 
            dispatch_async(dispatch_get_main_queue(), ^{                    
                NSError *error;
                if ([device lockForConfiguration:&error]) {
                    device.exposureMode = AVCaptureExposureModeLocked;
                    [device unlockForConfiguration];
                } else {
                    [self.delegate deviceConfigurationFailedWithError:error];
                }
            });
        }

    } else {
        [super observeValueForKeyPath:keyPath
                             ofObject:object
                               change:change
                              context:context];
    }
}

/* 恢复对焦和曝光设置 */
- (void)resetFocusAndExposureModes {

    AVCaptureDevice *device = self.activeVideoInput.device;

    AVCaptureExposureMode exposureMode =
    AVCaptureExposureModeContinuousAutoExposure;

    AVCaptureFocusMode focusMode = AVCaptureFocusModeContinuousAutoFocus;

    BOOL canResetFocus = [device isFocusPointOfInterestSupported] &&        
    [device isFocusModeSupported:focusMode];

    BOOL canResetExposure = [device isExposurePointOfInterestSupported] &&  
    [device isExposureModeSupported:exposureMode];

    CGPoint centerPoint = CGPointMake(0.5f, 0.5f);    // 创建一个中心扫描点.

    NSError *error;
    if ([device lockForConfiguration:&error]) {

        if (canResetFocus) {    // 焦点可以重置
            device.focusMode = focusMode;
            device.focusPointOfInterest = centerPoint;
        }

        if (canResetExposure) {    // 曝光可以充值
            device.exposureMode = exposureMode;
            device.exposurePointOfInterest = centerPoint;
        }
        
        [device unlockForConfiguration];
        
    } else {
        [self.delegate deviceConfigurationFailedWithError:error];
    }
}

调整闪光灯和手电筒模式(Flash和 Torch 模式)
AVCaptureDevice可以控制摄像头的LED灯,当拍照时是做闪光灯,当拍视频时做手电筒.

- (void)setFlashMode:(AVCaptureFlashMode)flashMode {

    AVCaptureDevice *device =  self.activeVideoInput.device;

    if (device.flashMode != flashMode &&
        [device isFlashModeSupported:flashMode]) {

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


- (void)setTorchMode:(AVCaptureTorchMode)torchMode {

    AVCaptureDevice *device = self.activeVideoInput.device;

    if (device.torchMode != torchMode &&
        [device isTorchModeSupported:torchMode]) {

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

3. 基本功能实现-拍照和摄像

拍照
上面介绍了基本流程,如果要拍照就是希望捕捉会话的输出Output实例是AVCaptureStillImageOutput类型,这需要在第一步配置会话时添加上去. 而关于接下来具体拍摄方法就定义在AVCaptureStillImageOutput中. 代码如下:

- (void)captureStillImage {
    // 获取Output对象当前使用的AVCaptureConnection连接.
    // 原始相机只支持垂直方向,所以当设备旋转时,用户界面保持不变.我们希望横向时相应调整图片方向.
    AVCaptureConnection *connection =                                   
        [self.imageOutput connectionWithMediaType:AVMediaTypeVideo];
        // 这里要先确定Connection 是否支持设置视频方向. 然后设置图片方向.
    if (connection.isVideoOrientationSupported) {    
        connection.videoOrientation = [self currentVideoOrientation];
    }
    

    id handler = ^(CMSampleBufferRef sampleBuffer, NSError *error) {
        if (sampleBuffer != NULL) {    
            NSData *imageData =
                [AVCaptureStillImageOutput
                    jpegStillImageNSDataRepresentation:sampleBuffer];
           // 得到的照片
            UIImage *image = [[UIImage alloc] initWithData:imageData];
        } else {
            NSLog(@"NULL sampleBuffer: %@", [error localizedDescription]);
        }
    };
    // 拍摄静态图片
    [self.imageOutput captureStillImageAsynchronouslyFromConnection:connection
                                                  completionHandler:handler];
}

视频
同拍照流程一样,设置捕捉会话的输出Output实例是 AVCaptureMovieFileOutput类型. 具体摄像代码如下:

- (void)startRecording {

    if (!self.movieOutput.isRecording) { // 是否在录制中
        // 设置录制视频方向为当前方向
        AVCaptureConnection *videoConnection =                              
            [self.movieOutput connectionWithMediaType:AVMediaTypeVideo];
        if ([videoConnection isVideoOrientationSupported]) {                
            videoConnection.videoOrientation = self.currentVideoOrientation;
        }
        // 设置VideoStabilization.可以提高视频质量.
        if ([videoConnection isVideoStabilizationSupported]) {              
            if ([[[UIDevice currentDevice] systemVersion] floatValue] < 8.0) {
                videoConnection.enablesVideoStabilizationWhenAvailable = YES;
            } else {
                videoConnection.preferredVideoStabilizationMode = AVCaptureVideoStabilizationModeAuto;
            }
        }

        AVCaptureDevice *device = self.activeVideoInput.device;
        // 设置平滑对焦模式,提升移动录制质量
        if (device.isSmoothAutoFocusSupported) {                            
            NSError *error;
            if ([device lockForConfiguration:&error]) {
                device.smoothAutoFocusEnabled = NO;
                [device unlockForConfiguration];
            } else {
                [self.delegate deviceConfigurationFailedWithError:error];
            }
        }

        NSURL *outputURL = [self uniqueURL];   // 定义视频文件唯一输出路径.        
        // 最后,开始录制. 通过AVCaptureFileOutputRecordingDelegate控制录制过程.
        [self.movieOutput startRecordingToOutputFileURL:outputURL      
                                      recordingDelegate:self];

    }
}

AVCaptureMovieFileOutput支持分段捕捉.

AVFoundation框架(五) 媒体捕捉上- 简单的录制

1. 媒体捕捉的类

2. 细节部分.

2.1 捕捉设备的修改与配置

3. 基本功能实现-拍照和摄像

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