媒体基础获取拓扑节点的 IMFMedia类型

>我写了一个基于SampleGrabberSink示例的应用程序。我的应用程序实际上可以按我想要的方式工作，但我需要执行的一个功能是在.mp4源在文件中部分更改时获得视频分辨率。我最终想出了如何做到这一点，但它似乎很冗长，我怀疑一定有更简单的方法。

在下面的示例中，有没有办法缩短处理MESessionStreamSinkFormatChanged情况的代码块？似乎需要近 40 行代码(计算初始化和清理(应该需要 1 或 2 行。

HRESULT RunSession(IMFMediaSession *pSession, IMFTopology *pTopology, OnVideoResolutionChangedFunc onVideoResolutionChanged)
{
IMFMediaEvent *pEvent = NULL;
IMFTopologyNode *pNode = nullptr;
IMFStreamSink *pStreamSink = nullptr;
IUnknown *pNodeObject = NULL;
IMFMediaTypeHandler *pMediaTypeHandler = nullptr;
IMFMediaType *pMediaType = nullptr;
PROPVARIANT var;
PropVariantInit(&var);
HRESULT hr = S_OK;
CHECK_HR(hr = pSession->SetTopology(0, pTopology));
CHECK_HR(hr = pSession->Start(&GUID_NULL, &var));
while(1)
{
HRESULT hrStatus = S_OK;
MediaEventType met;
CHECK_HR(hr = pSession->GetEvent(0, &pEvent));
CHECK_HR(hr = pEvent->GetStatus(&hrStatus));
CHECK_HR(hr = pEvent->GetType(&met));
if(FAILED(hrStatus))
{
printf("Session error: 0x%x (event id: %d)n", hrStatus, met);
hr = hrStatus;
goto done;
}
else
{
//printf("Session event: event id: %dn",  met);
switch(met)
{
case MESessionStreamSinkFormatChanged:
//std::cout << "MESessionStreamSinkFormatChanged." << std::endl;
{
MF_TOPOLOGY_TYPE nodeType;
UINT64 outputNode{0};
GUID majorMediaType;
UINT64 videoResolution{0};
UINT32 stride{0};
// This seems a ridiculously convoluted way to extract the change to the video resolution. There may
// be a simpler way but then again this is the Media Foundation and COM!
CHECK_HR_ERROR(pEvent->GetUINT64(MF_EVENT_OUTPUT_NODE, &outputNode), "Failed to get ouput node from media changed event.");
CHECK_HR_ERROR(pTopology->GetNodeByID(outputNode, &pNode), "Failed to get topology node for output ID.");
CHECK_HR_ERROR(pNode->GetObject(&pNodeObject), "Failed to get the node's object pointer.");
CHECK_HR_ERROR(pNodeObject->QueryInterface(IID_PPV_ARGS(&pStreamSink)), "Failed to get media stream sink from activation object.");
CHECK_HR_ERROR(pStreamSink->GetMediaTypeHandler(&pMediaTypeHandler), "Failed to get media type handler from stream sink.");
CHECK_HR_ERROR(pMediaTypeHandler->GetCurrentMediaType(&pMediaType), "Failed to get current media type.");
CHECK_HR_ERROR(pMediaType->GetMajorType(&majorMediaType), "Failed to get major media type.");
if(majorMediaType == MFMediaType_Video)
{
CHECK_HR_ERROR(pMediaType->GetUINT64(MF_MT_FRAME_SIZE, &videoResolution), "Failed to get new video resolution.");
CHECK_HR_ERROR(pMediaType->GetUINT32(MF_MT_DEFAULT_STRIDE, &stride), "Failed to get the new stride.");
std::cout << "Media session video resolution changed to width " << std::to_string(HI32(videoResolution)) 
<< " and height " << std::to_string(LO32(videoResolution)) 
<< " and stride " << stride << "." << std::endl;
if(onVideoResolutionChanged != nullptr) {
onVideoResolutionChanged(HI32(videoResolution), LO32(videoResolution), stride);
}
}
break;
}
default:
break;
}
}
if(met == MESessionEnded)
{
break;
}
SafeRelease(&pEvent);
SafeRelease(&pNode);
SafeRelease(&pStreamSink);
SafeRelease(&pNodeObject);
SafeRelease(&pMediaTypeHandler);
SafeRelease(&pMediaType);
}
done:
SafeRelease(&pEvent);
SafeRelease(&pNode);
SafeRelease(&pStreamSink);
SafeRelease(&pNodeObject);
SafeRelease(&pMediaTypeHandler);
SafeRelease(&pMediaType);
return hr;
}