视频录制功能(FileOutput/AVAssetWriter)

FileOutput(封装前后摄像头，闪光灯，分辨率设置，焦距，设置帧率，调节ISO，光感度 0.0-1.0，横竖屏切换)

由于公司需求 视频录制需要自定义视频码率 使用AVCaptureFileOutput只能实现视频帧率更改
所以更改项目功能 使用AVAssetWriter来实现

基本思路

使用

AVCaptureVideoDataOutput//视频输
AVCaptureAudioDataOutput//音频输出
AVCaptureVideoDataOutputSampleBufferDelegate
AVCaptureAudioDataOutputSampleBufferDelegate

在代理(参考 http://blog.imwcl.com/2016/05/25/iOS%E5%BC%80%E5%8F%91%E8%BF%9B%E9%98%B6%20-%20%E7%94%A8AVFoundation%E8%87%AA%E5%AE%9A%E4%B9%89%E8%A7%86%E9%A2%91%E5%BD%95%E5%88%B6%E5%8A%9F%E8%83%BD/)

逻辑思路
根据代理获取CMSampleBufferRef 获取视频帧，通过AVAssetWriter媒体写入对象，更改视频码率编码

 videoCompressionProps = [NSDictionary dictionaryWithObjectsAndKeys:
                                         [NSNumber numberWithInteger:FrameRate], AVVideoMaxKeyFrameIntervalKey,
                                         [NSNumber numberWithInteger:BitRate], AVVideoAverageBitRateKey,
                                         AVVideoH264EntropyModeCABAC,AVVideoH264EntropyModeKey,
                                         nil];
    
    videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                     AVVideoCodecH264,AVVideoCodecKey,
                     videoCompressionProps, AVVideoCompressionPropertiesKey,
                     AVVideoScalingModeResizeAspectFill,AVVideoScalingModeKey,
                     [NSNumber numberWithInteger:videoWight],AVVideoWidthKey,
                     [NSNumber numberWithInteger:videoHeight],AVVideoHeightKey,
                     nil];

    //初始化视频写入类
    _videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
    //表明输入是否应该调整其处理为实时数据源的数据
    _videoInput.expectsMediaDataInRealTime = YES;
    //将视频输入源加入
    [_writer addInput:_videoInput];

通过获取CMSampleBufferRef的时间节点 调整timeOffset

CMSampleBufferGetPresentationTimeStamp

开始不断的进行拼接视频帧数据

 //获取开始写入的CMTime
 CMTime startTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
//开始写入
 [_writer startWriting];
 [_writer startSessionAtSourceTime:startTime];

下面是具体封装的demo

https://github.com/qw9685/Two-methods-of-video-recording