SCRecorder(一)：SCRecorder类

快速使用

SCRecorder *recorder = [SCRecorder recorder]; // You can also use +[SCRecorder sharedRecorder]
if (![recorder startRunning]) {
    NSLog(@"Something wrong there: %@", recorder.error);
}
recorder.session = [SCRecordSession recordSession];
[recorder record];
[recorder pause];

SCRecorder

init方法

_sessionQueue = dispatch_queue_create("me.corsin.SCRecorder.RecordSession", nil);

创建一个_sessionQueue队列，用于向SCRecordSession发送信息

dispatch_queue_set_specific方法向指定的_sessionQueue设置一个kSCRecorderRecordSessionQueueKey的标识，这两个方法可以解决GCD方法可重入问题，这里还有一个说UI线程操作的例子。

dispatch_set_target_queue(_sessionQueue, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));

dispatch_set_target_queue除了能用来设置队列的优先级之外，还能够创建队列的层次体系，当我们想让不同队列中的任务同步的执行时，我们可以创建一个串行队列，然后将这些队列的target指向新创建的队列即可。
在这里，把_sessionQueue的优先级设为跟dispatch_get_global_queue一样的优先级。

事件通知方法

一系列在init时注册的通知方法

屏幕旋转方法

//都是私有方法
- (void)updateVideoOrientation;
- (AVCaptureVideoOrientation)actualVideoOrientation;

准备session和配置输入输出

关于输入输出配置的问题看另一篇文章

1 - (BOOL)prepare:(NSError **)error 
2 - (void)beginConfiguration
3 - (void)commitConfiguration
4 - (BOOL)_reconfigureSession
5 - (void)reconfigureVideoInput:(BOOL)shouldConfigureVideo audioInput:(BOOL)shouldConfigureAudio
6 - (void)configureDevice:(AVCaptureDevice*)newDevice mediaType:(NSString*)mediaType error:(NSError**)error
7 - (AVCaptureDeviceInput*)currentDeviceInputForMediaType:(NSString*)mediaType

方法1用来初始化AVCaptureSession，然后依次调用2、4、5、3
方法2/3不提
方法4：
- 设置sessionPreset
- 根据fastRecordMethodEnabled属性设置AVCaptureVideoDataOutput,AVCaptureAudioDataOutput,AVCaptureMovieFileOutput,AVCaptureStillImageOutput四种响应链终点类
方法5/6/7：根据shouldConfigureVideo和shouldConfigureAudio两个参数确定是否重新配置AVCaptureDevice和AVCaptureDeviceInput，并重新添加到captureSession中

session开始预览视频

- (BOOL)startRunning
- (void)stopRunning

两个方法里调用AVCaptureSession的startRunning和stopRunning方法

录制和暂停

SCRecorder录制暂停.png

1 - (void)record 
2 - (void)_progressTimerFired:(NSTimer *)progressTimer
3 - (void)pause
4 - (void)pause:(void(^)())completionHandler
5 - (NSDictionary *)_createSegmentInfo

无论录制还是暂停方法，都要在_sessionQueue执行相关block，所以有下段代码

 if ([SCRecorder isSessionQueue]) {
        block();
    } else {
        dispatch_sync(_sessionQueue, block);
    }

方法一：经由- (void)beginRecordSegmentIfNeeded:(SCRecordSession *)recordSession方法到SCRecordSession使movieFileOutput开始录制到指定url
方法二：不提
方法三、四：经由SCRecordSession使停止录制并把录制段落添加到_segments数组中

AVCaptureAudioDataOutputSampleBufferDelegate和AVCaptureVideoDataOutputSampleBufferDelegate处理流程

音视频sample处理流程.png

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection 
- (void)_handleVideoSampleBuffer:(CMSampleBufferRef)sampleBuffer withSession:(SCRecordSession *)recordSession connection:(AVCaptureConnection *)connection 
- (void)_handleAudioSampleBuffer:(CMSampleBufferRef)sampleBuffer withSession:(SCRecordSession *)recordSession
- (void)appendVideoSampleBuffer:(CMSampleBufferRef)sampleBuffer toRecordSession:(SCRecordSession *)recordSession duration:(CMTime)duration connection:(AVCaptureConnection *)connection completion:(void(^)(BOOL success))completion 
- (SCFilter *)_transformFilterUsingBufferWidth:(size_t)bufferWidth bufferHeight:(size_t)bufferHeight mirrored:(BOOL)mirrored

AVCaptureFileOutputRecordingDelegate

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

SCRecorder(一)：SCRecorder类