AVFoundation（四）滤镜视频录制流程

https://www.jianshu.com/p/4701d006b514

核心思路

1. GPUImageVideoCamera    采集视频： CMSampleBufferRef
                                                  采集音频：CMSampleBufferRef

2. 渲染滤镜：filter

3. 输出： 显示 GPUImageView
                 写入视频 GPUImageMovieWriter      

1.  连接视频滤镜

// 摄像头
   _videoCamera = [[GPUImageVideoCamera alloc] initWithSessionPreset:AVCaptureSessionPreset640x480 cameraPosition:AVCaptureDevicePositionBack];
   _videoCamera.outputImageOrientation = [UIApplication sharedApplication].statusBarOrientation;
    
  // 滤镜
   _filter = [[GPUImageSepiaFilter alloc] init];
   _filterView = [[GPUImageView alloc] initWithFrame:self.view.frame];
   self.view = _filterView;
    
  // 响应链
   [_videoCamera addTarget:_filter];
   [_filter addTarget:_filterView];
   [_videoCamera startCameraCapture];

2. 开始录制

_movieWriter = [[GPUImageMovieWriter alloc] initWithMovieURL:movieURL size:CGSizeMake(480.0, 640.0)];
        _movieWriter.encodingLiveVideo = YES;
        [_filter addTarget:_movieWriter];
        _videoCamera.audioEncodingTarget = _movieWriter;
        [_movieWriter startRecording];

3. 结束录制

[_filter removeTarget:_movieWriter];
_videoCamera.audioEncodingTarget = nil;
[_movieWriter finishRecording];