[Microsoft Media Foundation]Requirements which enable MF_READWRITE_ENABLE_HARDWARE_TRANSFORMS parameter

I am trying an encoding program on Windows 8.1/Visual C++ 2013 by referring this page. I tried various ways in the combination of MFVideoFormat_H264 and MFAudioFormat_AAC with MF_READWRITE_ENABLE_HARDWARE_TRANSFORMS parameter. However, when IMFSinkWriter::WriteSample is called, it consumes many CPU resources. 

That seems hardly processing hardware. Isn't this function supported yet in Windows 8, or is it a pre-processing required for this program? 

IMFAttributes *spattr = NULL;
MFCreateAttributes(&spattr, 10);
spattr->SetUINT32(MF_READWRITE_ENABLE_HARDWARE_TRANSFORMS, TRUE);
//spattr->SetUINT32(MF_READWRITE_DISABLE_CONVERTERS, FALSE);
spattr->SetUINT32(MF_LOW_LATENCY, TRUE);
spattr->SetGUID(MF_TRANSCODE_CONTAINERTYPE, MFTranscodeContainerType_MPEG4);

hr = MFCreateSinkWriterFromURL(path, NULL, spattr, &writer);