video压缩ios：使用AVAssetWriter缩小video的大小

我成功地使用AVAssetWriter和AVAssetWriterInput将由AVFoundation Framework的AVCaptureVideoPreviewLayer捕获的一系列图像编码为video。

但是video的大小太大了，在这种情况下，你们中的任何一个人都可以给我一个教程或者是一个直接的我，或者给我正确的video输出设置来进行video压缩。

我正在使用以下VideoOutputSetting。

videoOutputSettings = @{ AVVideoCodecKey: AVVideoCodecH264, AVVideoWidthKey: [NSNumber numberWithInt:width], AVVideoHeightKey: [NSNumber numberWithInt:height], AVVideoCompressionPropertiesKey: @{ AVVideoAverageBitRateKey: [NSNumber numberWithInt:bitrate], AVVideoMaxKeyFrameIntervalKey: @(150), AVVideoProfileLevelKey: AVVideoProfileLevelH264BaselineAutoLevel, AVVideoAllowFrameReorderingKey: @NO, AVVideoH264EntropyModeKey: AVVideoH264EntropyModeCAVLC, AVVideoExpectedSourceFrameRateKey: @(30), AVVideoAverageNonDroppableFrameRateKey: @(30) } }; videoWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings]; _videoWriterInput.expectsMediaDataInRealTime = YES;