c++ - OSX，VideoToolbox，压缩 session

环境

OSX优胜美地

xcode 6.4

C++

用例
给定一个由单个关键帧和多个对应的增量帧组成的h264 GOP，对GOP进行解码，然后对单个 4.2Mbit 关键帧进行编码
问题描述
我能够解码GOP并对关键帧进行编码，但是，生成的关键帧的质量较低(低比特率)，也就是说，尽管我专门将比特率设置为4.2Mbit(这可以可以在下面的代码中看到)，记住我只需要一个单个关键帧，有什么方法可以设置VideoToolBox编码器以输出高比特率关键帧？

const CMVideoCodecType  fourcc  = (CMVideoCodecType)CMVideoFormatDescriptionGetCodecType(fmt);

// Else, generate a h264 KeyFrame

CFObjectSmartPtr< CFMutableDictionaryRef >  dictEncSpec;
dictEncSpec.Attach(CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks));
//dictEncSpec.Attach(CFDictionaryCreateMutable(NULL, 0, 0, 0));
// CFDictionarySetNumVal(dictEncSpec, kVTVideoEncoderSpecification_RequireHardwareAcceleratedVideoEncoder, TRUE);
CFDictionarySetValue(dictEncSpec, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_High_3_2);
// CFDictionarySetValue(dictEncSpec, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);

// CFDictionarySetValue(dictEncSpec, kVTCompressionPropertyKey_H264EntropyMode, kVTH264EntropyMode_CABAC);

CFDictionarySetNumVal(dictEncSpec, kVTCompressionPropertyKey_AverageBitRate, 4200000);
CFDictionarySetNumVal(dictEncSpec, kVTCompressionPropertyKey_Quality, 1.0f);
CFDictionarySetNumVal(dictEncSpec, kVTCompressionPropertyKey_MaxFrameDelayCount, 0);
CFDictionarySetNumVal(dictEncSpec, kVTCompressionPropertyKey_MaxKeyFrameIntervalDuration, 1);
CFDictionarySetNumVal(dictEncSpec, kVTCompressionPropertyKey_ExpectedDuration, 1);
CFDictionarySetNumVal(dictEncSpec, kVTCompressionPropertyKey_ExpectedFrameRate, 10);
// CFDictionarySetNumVal(dictEncSpec, kVTCompressionPropertyKey_SourceFrameCount, 1);
CFDictionarySetNumVal(dictEncSpec, kVTVideoEncoderSpecification_EnableHardwareAcceleratedVideoEncoder, TRUE);

CFObjectSmartPtr< VTCompressionSessionRef > sessionCompression;
status = VTCompressionSessionCreate(0, res.width, res.height, fourcc, (CFDictionaryRef)dictEncSpec, 0, 0, CompressionCallback, &ctx, &sessionCompression);
if (noErr != status)
    return HRESULT_FROM_ERRNO(status);
if (noErr != (status = VTCompressionSessionEncodeFrame(sessionCompression, ctx.yuvFrame, timestamp, timestamp, 0, 0, 0)))
    return HRESULT_FROM_ERRNO(status);
if(noErr != (status = VTCompressionSessionCompleteFrames(sessionCompression, timestamp)))
    return HRESULT_FROM_ERRNO(status);
if (0 == ctx.keyFrame) {
    assert(false);
    return E_UNEXPECTED;
}

ctx.keyFrame 最终质量很低

最佳答案

创建VTCompressionSession之后，还需要考虑另一个因素，您需要在VTCompressionSessionEncodeFrame中正确设置帧时间戳。

关于c++ - OSX，VideoToolbox，压缩 session ，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/31567639/