ISpStream::SetBaseStream を見てください。ここに小さなヘルパーがあります:
inline HRESULT SPCreateStreamOnHGlobal(
HGLOBAL hGlobal, //Memory handle for the stream object
BOOL fDeleteOnRelease, //Whether to free memory when the object is released
const WAVEFORMATEX * pwfex, //WaveFormatEx for stream
ISpStream ** ppStream) //Address of variable to receive ISpStream pointer
{
HRESULT hr;
IStream * pMemStream;
*ppStream = NULL;
hr = ::CreateStreamOnHGlobal(hGlobal, fDeleteOnRelease, &pMemStream);
if (SUCCEEDED(hr))
{
hr = ::CoCreateInstance(CLSID_SpStream, NULL, CLSCTX_ALL, __uuidof(*ppStream), (void **)ppStream);
if (SUCCEEDED(hr))
{
hr = (*ppStream)->SetBaseStream(pMemStream, SPDFID_WaveFormatEx, pwfex);
if (FAILED(hr))
{
(*ppStream)->Release();
*ppStream = NULL;
}
}
pMemStream->Release();
}
return hr;
}