use phonon crash in phonon_ds9d4.dll - qt

Question

use code :
Phonon::VideoPlayer *player = new Phonon::VideoPlayer(Phonon::MusicCategory, NULL);
QObject::connect(player, SIGNAL(finished()), player, SLOT(deleteLater()));
player->play(Phonon::MediaSource("c:/yaodong.mkv"));
but crash.
env is win7 and vs2008, qt 4.7.1
windows sdk is 7.1
dx sdk is Microsoft DirectX SDK (March 2009)
and i find the stack is
mediaobject.cpp (line 233) graph is null
} else if (!m_currentWork.url.isEmpty()) {
//let's render a url (blocking call)
hr = m_currentWork.graph->RenderFile(reinterpret_cast<const wchar_t *>(m_currentWork.url.utf16()), 0);
}
then i find run step to the function:
quint16 WorkerThread::addUrlToRender(const QString &url)
{
QMutexLocker locker(&m_mutex);
Work w;
w.task = Render;
//we create a new graph
w.graph = Graph(CLSID_FilterGraph, IID_IGraphBuilder);
w.url = url;
w.url.detach();
w.id = m_currentWorkId++;
m_queue.enqueue(w);
m_waitCondition.set();
return w.id;
}
the line : w.graph = Graph(CLSID_FilterGraph, IID_IGraphBuilder);
w.graph is null.
but i wrote the code outside :
IGraphBuilder *pGraph = NULL;
::CoCreateInstance(CLSID_FilterGraph, 0, CLSCTX_INPROC_SERVER, IID_IGraphBuilder,
reinterpret_cast<void**>(&pGraph));
the pGraph is not null.
help. thanks!