AVAssetWriter 和 AVAssetWriterInp

AVAssetWriter 可以添加 AVAssetWriterInput
AVAssetWriterInput 分文好几种类型
可以直接 接受buffer 来录制成视频和声音文件
多段视频就是这个道理
配置如下

/**
 *  设置写入视频属性
 */
- (void)setUpWriter
{
    if (self.videoURL == nil)
    {
        return;
    }
    
    self.assetWriter = [AVAssetWriter assetWriterWithURL:self.videoURL fileType:AVFileTypeMPEG4 error:nil];
    //写入视频大小
    NSInteger numPixels = kScreenWidth * kScreenHeight;
    
    //每像素比特
    CGFloat bitsPerPixel = 12.0;
    NSInteger bitsPerSecond = numPixels * bitsPerPixel;
    
    // 码率和帧率设置
    NSDictionary *compressionProperties = @{ AVVideoAverageBitRateKey : @(bitsPerSecond),
                                             AVVideoExpectedSourceFrameRateKey : @(15),
                                             AVVideoMaxKeyFrameIntervalKey : @(15),
                                             AVVideoProfileLevelKey : AVVideoProfileLevelH264BaselineAutoLevel };
    CGFloat width = kScreenWidth;
    CGFloat height = kScreenHeight;
    
    //视频属性
    NSDictionary *videoCompressionSettings = @{ AVVideoCodecKey : AVVideoCodecTypeH264,
                                                AVVideoWidthKey : @(width * 2),
                                                AVVideoHeightKey : @(height * 2),
                                                AVVideoScalingModeKey : AVVideoScalingModeResizeAspectFill,
                                                AVVideoCompressionPropertiesKey : compressionProperties };
    
    _assetWriterVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
    //expectsMediaDataInRealTime 必须设为yes，需要从capture session 实时获取数据
    _assetWriterVideoInput.expectsMediaDataInRealTime = YES;
    
    // 音频设置
    NSDictionary *audioCompressionSettings = @{ AVEncoderBitRatePerChannelKey : @(28000),
                                                AVFormatIDKey : @(kAudioFormatMPEG4AAC),
                                                AVNumberOfChannelsKey : @(1),
                                                AVSampleRateKey : @(22050) };
    
    _assetWriterAudioInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:audioCompressionSettings];
    
    _assetWriterAudioInput.expectsMediaDataInRealTime = YES;
    
    if ([_assetWriter canAddInput:_assetWriterVideoInput])
    {
        [_assetWriter addInput:_assetWriterVideoInput];
    }
    else
    {
        NSLog(@"AssetWriter videoInput append Failed");
    }
    
    if ([_assetWriter canAddInput:_assetWriterAudioInput])
    {
        [_assetWriter addInput:_assetWriterAudioInput];
    }
    else
    {
        NSLog(@"AssetWriter audioInput Append Failed");
    }
    
    _canWrite = NO;
}