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Using the Sample Grabber Sink

The Sample Grabber Sink is a media sink that forwards the data it receives to an application callback interface.

Note The Source Reader is an alternative to the Sample Grabber Sink and has a simpler progamming model.

1. Implement the Callback Interface


// The class that implements the callback interface.
class SampleGrabberCB : public IMFSampleGrabberSinkCallback 
{
    long m_cRef;

    SampleGrabberCB() : m_cRef(1) {}

public:
    static HRESULT CreateInstance(SampleGrabberCB **ppCB);

    // IUnknown methods
    STDMETHODIMP QueryInterface(REFIID iid, void** ppv);
    STDMETHODIMP_(ULONG) AddRef();
    STDMETHODIMP_(ULONG) Release();

    // IMFClockStateSink methods
    STDMETHODIMP OnClockStart(MFTIME hnsSystemTime, LONGLONG llClockStartOffset);
    STDMETHODIMP OnClockStop(MFTIME hnsSystemTime);
    STDMETHODIMP OnClockPause(MFTIME hnsSystemTime);
    STDMETHODIMP OnClockRestart(MFTIME hnsSystemTime);
    STDMETHODIMP OnClockSetRate(MFTIME hnsSystemTime, float flRate);

    // IMFSampleGrabberSinkCallback methods
    STDMETHODIMP OnSetPresentationClock(IMFPresentationClock* pClock);
    STDMETHODIMP OnProcessSample(REFGUID guidMajorMediaType, DWORD dwSampleFlags,
        LONGLONG llSampleTime, LONGLONG llSampleDuration, const BYTE * pSampleBuffer,
        DWORD dwSampleSize);
    STDMETHODIMP OnShutdown();
};

2. Create the Sample Grabber Sink

C++


    CHECK_HR(hr = MFCreateMediaType(&pType));
    CHECK_HR(hr = pType->SetGUID(MF_MT_MAJOR_TYPE, MFMediaType_Audio));
    CHECK_HR(hr = pType->SetGUID(MF_MT_SUBTYPE, MFAudioFormat_PCM));

    // Create the sample grabber sink.
    CHECK_HR(hr = SampleGrabberCB::CreateInstance(&pCallback));
    CHECK_HR(hr = MFCreateSampleGrabberSinkActivate(pType, pCallback, &pSinkActivate));

    // To run as fast as possible, set this attribute (requires Windows 7):
    CHECK_HR(hr = pSinkActivate->SetUINT32(MF_SAMPLEGRABBERSINK_IGNORE_CLOCK, TRUE));

3. Create a Topology

C++


// Create the topology.
HRESULT CreateTopology(IMFMediaSource *pSource, IMFActivate *pSinkActivate, IMFTopology **ppTopo)
{
    IMFTopology *pTopology = NULL;
    IMFPresentationDescriptor *pPD = NULL;
    IMFStreamDescriptor *pSD = NULL;
    IMFMediaTypeHandler *pHandler = NULL;
    IMFTopologyNode *pNode1 = NULL;
    IMFTopologyNode *pNode2 = NULL;

    HRESULT hr = S_OK;
    DWORD cStreams = 0;

    CHECK_HR(hr = MFCreateTopology(&pTopology));
    CHECK_HR(hr = pSource->CreatePresentationDescriptor(&pPD));
    CHECK_HR(hr = pPD->GetStreamDescriptorCount(&cStreams));
    
    for (DWORD i = 0; i < cStreams; i++)
    {
        // In this example, we look for audio streams and connect them to the sink.

        BOOL fSelected = FALSE;
        GUID majorType;

        CHECK_HR(hr = pPD->GetStreamDescriptorByIndex(i, &fSelected, &pSD));
        CHECK_HR(hr = pSD->GetMediaTypeHandler(&pHandler));
        CHECK_HR(hr = pHandler->GetMajorType(&majorType));

        if (majorType == MFMediaType_Audio && fSelected)
        {
            CHECK_HR(hr = AddSourceNode(pTopology, pSource, pPD, pSD, &pNode1));
            CHECK_HR(hr = AddOutputNode(pTopology, pSinkActivate, 0, &pNode2));
            CHECK_HR(hr = pNode1->ConnectOutput(0, pNode2, 0));
            break;
        }
        else
        {
            CHECK_HR(hr = pPD->DeselectStream(i));
        }
        SafeRelease(&pSD);
        SafeRelease(&pHandler);
    }

    *ppTopo = pTopology;
    (*ppTopo)->AddRef();

done:
    SafeRelease(&pTopology);
    SafeRelease(&pNode1);
    SafeRelease(&pNode2);
    SafeRelease(&pPD);
    SafeRelease(&pSD);
    SafeRelease(&pHandler);
    return hr;
}

4. Run the Media Session

C++


HRESULT RunSession(IMFMediaSession *pSession, IMFTopology *pTopology)
{
    IMFMediaEvent *pEvent = NULL;

    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;
        }
        if (met == MESessionEnded)
        {
            break;
        }
        SafeRelease(&pEvent);
    }

done:
    SafeRelease(&pEvent);
    return hr;
}

Example Code

Here is the complete example code for this topic.

C++


#include <new>
#include <windows.h>
#include <mfapi.h>
#include <mfidl.h>
#include <Shlwapi.h>
#include <stdio.h>

#pragma comment(lib, "mfplat")
#pragma comment(lib, "mf")
#pragma comment(lib, "mfuuid")
#pragma comment(lib, "Shlwapi")

template <class T> void SafeRelease(T **ppT)
{
    if (*ppT)
    {
        (*ppT)->Release();
        *ppT = NULL;
    }
}

#define CHECK_HR(x) if (FAILED(x)) { goto done; }

// The class that implements the callback interface.
class SampleGrabberCB : public IMFSampleGrabberSinkCallback 
{
    long m_cRef;

    SampleGrabberCB() : m_cRef(1) {}

public:
    static HRESULT CreateInstance(SampleGrabberCB **ppCB);

    // IUnknown methods
    STDMETHODIMP QueryInterface(REFIID iid, void** ppv);
    STDMETHODIMP_(ULONG) AddRef();
    STDMETHODIMP_(ULONG) Release();

    // IMFClockStateSink methods
    STDMETHODIMP OnClockStart(MFTIME hnsSystemTime, LONGLONG llClockStartOffset);
    STDMETHODIMP OnClockStop(MFTIME hnsSystemTime);
    STDMETHODIMP OnClockPause(MFTIME hnsSystemTime);
    STDMETHODIMP OnClockRestart(MFTIME hnsSystemTime);
    STDMETHODIMP OnClockSetRate(MFTIME hnsSystemTime, float flRate);

    // IMFSampleGrabberSinkCallback methods
    STDMETHODIMP OnSetPresentationClock(IMFPresentationClock* pClock);
    STDMETHODIMP OnProcessSample(REFGUID guidMajorMediaType, DWORD dwSampleFlags,
        LONGLONG llSampleTime, LONGLONG llSampleDuration, const BYTE * pSampleBuffer,
        DWORD dwSampleSize);
    STDMETHODIMP OnShutdown();
};

HRESULT CreateMediaSource(PCWSTR pszURL, IMFMediaSource **ppSource);
HRESULT CreateTopology(IMFMediaSource *pSource, IMFActivate *pSink, IMFTopology **ppTopo);
HRESULT RunSession(IMFMediaSession *pSession, IMFTopology *pTopology);

HRESULT RunSampleGrabber(PCWSTR pszFileName)
{
    IMFMediaSession *pSession = NULL;
    IMFMediaSource *pSource = NULL;
    SampleGrabberCB *pCallback = NULL;
    IMFActivate *pSinkActivate = NULL;
    IMFTopology *pTopology = NULL;
    IMFMediaType *pType = NULL;

    // Configure the media type that the Sample Grabber will receive.
    // Setting the major and subtype is usually enough for the topology loader
    // to resolve the topology.

    CHECK_HR(hr = MFCreateMediaType(&pType));
    CHECK_HR(hr = pType->SetGUID(MF_MT_MAJOR_TYPE, MFMediaType_Audio));
    CHECK_HR(hr = pType->SetGUID(MF_MT_SUBTYPE, MFAudioFormat_PCM));

    // Create the sample grabber sink.
    CHECK_HR(hr = SampleGrabberCB::CreateInstance(&pCallback));
    CHECK_HR(hr = MFCreateSampleGrabberSinkActivate(pType, pCallback, &pSinkActivate));

    // To run as fast as possible, set this attribute (requires Windows 7):
    CHECK_HR(hr = pSinkActivate->SetUINT32(MF_SAMPLEGRABBERSINK_IGNORE_CLOCK, TRUE));

    // Create the Media Session.
    HRESULT hr = S_OK;
    CHECK_HR(hr = MFCreateMediaSession(NULL, &pSession));

    // Create the media source.
    CHECK_HR(hr = CreateMediaSource(pszFileName, &pSource));

    // Create the topology.
    CHECK_HR(hr = CreateTopology(pSource, pSinkActivate, &pTopology));

    // Run the media session.
    CHECK_HR(hr = RunSession(pSession, pTopology));

done:
    // Clean up.
    if (pSource)
    {
        pSource->Shutdown();
    }
    if (pSession)
    {
        pSession->Shutdown();
    }

    SafeRelease(&pSession);
    SafeRelease(&pSource);
    SafeRelease(&pCallback);
    SafeRelease(&pSinkActivate);
    SafeRelease(&pTopology);
    SafeRelease(&pType);
    return hr;
}

int wmain(int argc, wchar_t* argv[])
{
    HRESULT hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);
    if (SUCCEEDED(hr))
    {
        hr = MFStartup(MF_VERSION);
        if (SUCCEEDED(hr))
        {
            hr = RunSampleGrabber(argv[1]);
            MFShutdown();
        }
        CoUninitialize();
    }
    return 0;
}

// Create a media source from a URL.
HRESULT CreateMediaSource(PCWSTR pszURL, IMFMediaSource **ppSource)
{
    IMFSourceResolver* pSourceResolver = NULL;
    IUnknown* pSource = NULL;

    // Create the source resolver.
    HRESULT hr = S_OK;
    CHECK_HR(hr = MFCreateSourceResolver(&pSourceResolver));

    MF_OBJECT_TYPE ObjectType;
    CHECK_HR(hr = pSourceResolver->CreateObjectFromURL(pszURL,                     
        MF_RESOLUTION_MEDIASOURCE, NULL, &ObjectType, &pSource));

    hr = pSource->QueryInterface(IID_PPV_ARGS(ppSource));

done:
    SafeRelease(&pSourceResolver);
    SafeRelease(&pSource);
    return hr;
}


// Add a source node to a topology.
HRESULT AddSourceNode(
    IMFTopology *pTopology,           // Topology.
    IMFMediaSource *pSource,          // Media source.
    IMFPresentationDescriptor *pPD,   // Presentation descriptor.
    IMFStreamDescriptor *pSD,         // Stream descriptor.
    IMFTopologyNode **ppNode)         // Receives the node pointer.
{
    IMFTopologyNode *pNode = NULL;

    HRESULT hr = S_OK;
    CHECK_HR(hr = MFCreateTopologyNode(MF_TOPOLOGY_SOURCESTREAM_NODE, &pNode));
    CHECK_HR(hr = pNode->SetUnknown(MF_TOPONODE_SOURCE, pSource));
    CHECK_HR(hr = pNode->SetUnknown(MF_TOPONODE_PRESENTATION_DESCRIPTOR, pPD));
    CHECK_HR(hr = pNode->SetUnknown(MF_TOPONODE_STREAM_DESCRIPTOR, pSD));
    CHECK_HR(hr = pTopology->AddNode(pNode));

    // Return the pointer to the caller.
    *ppNode = pNode;
    (*ppNode)->AddRef();

done:
    SafeRelease(&pNode);
    return hr;
}

// Add an output node to a topology.
HRESULT AddOutputNode(
    IMFTopology *pTopology,     // Topology.
    IMFActivate *pActivate,     // Media sink activation object.
    DWORD dwId,                 // Identifier of the stream sink.
    IMFTopologyNode **ppNode)   // Receives the node pointer.
{
    IMFTopologyNode *pNode = NULL;

    HRESULT hr = S_OK;
    CHECK_HR(hr = MFCreateTopologyNode(MF_TOPOLOGY_OUTPUT_NODE, &pNode));
    CHECK_HR(hr = pNode->SetObject(pActivate));
    CHECK_HR(hr = pNode->SetUINT32(MF_TOPONODE_STREAMID, dwId));
    CHECK_HR(hr = pNode->SetUINT32(MF_TOPONODE_NOSHUTDOWN_ON_REMOVE, FALSE));
    CHECK_HR(hr = pTopology->AddNode(pNode));

    // Return the pointer to the caller.
    *ppNode = pNode;
    (*ppNode)->AddRef();

done:
    SafeRelease(&pNode);
    return hr;
}

// Create the topology.
HRESULT CreateTopology(IMFMediaSource *pSource, IMFActivate *pSinkActivate, IMFTopology **ppTopo)
{
    IMFTopology *pTopology = NULL;
    IMFPresentationDescriptor *pPD = NULL;
    IMFStreamDescriptor *pSD = NULL;
    IMFMediaTypeHandler *pHandler = NULL;
    IMFTopologyNode *pNode1 = NULL;
    IMFTopologyNode *pNode2 = NULL;

    HRESULT hr = S_OK;
    DWORD cStreams = 0;

    CHECK_HR(hr = MFCreateTopology(&pTopology));
    CHECK_HR(hr = pSource->CreatePresentationDescriptor(&pPD));
    CHECK_HR(hr = pPD->GetStreamDescriptorCount(&cStreams));
    
    for (DWORD i = 0; i < cStreams; i++)
    {
        // In this example, we look for audio streams and connect them to the sink.

        BOOL fSelected = FALSE;
        GUID majorType;

        CHECK_HR(hr = pPD->GetStreamDescriptorByIndex(i, &fSelected, &pSD));
        CHECK_HR(hr = pSD->GetMediaTypeHandler(&pHandler));
        CHECK_HR(hr = pHandler->GetMajorType(&majorType));

        if (majorType == MFMediaType_Audio && fSelected)
        {
            CHECK_HR(hr = AddSourceNode(pTopology, pSource, pPD, pSD, &pNode1));
            CHECK_HR(hr = AddOutputNode(pTopology, pSinkActivate, 0, &pNode2));
            CHECK_HR(hr = pNode1->ConnectOutput(0, pNode2, 0));
            break;
        }
        else
        {
            CHECK_HR(hr = pPD->DeselectStream(i));
        }
        SafeRelease(&pSD);
        SafeRelease(&pHandler);
    }

    *ppTopo = pTopology;
    (*ppTopo)->AddRef();

done:
    SafeRelease(&pTopology);
    SafeRelease(&pNode1);
    SafeRelease(&pNode2);
    SafeRelease(&pPD);
    SafeRelease(&pSD);
    SafeRelease(&pHandler);
    return hr;
}

HRESULT RunSession(IMFMediaSession *pSession, IMFTopology *pTopology)
{
    IMFMediaEvent *pEvent = NULL;

    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;
        }
        if (met == MESessionEnded)
        {
            break;
        }
        SafeRelease(&pEvent);
    }

done:
    SafeRelease(&pEvent);
    return hr;
}

// SampleGrabberCB implementation

// Create a new instance of the object.
HRESULT SampleGrabberCB::CreateInstance(SampleGrabberCB **ppCB)
{
    *ppCB = new (std::nothrow) SampleGrabberCB();

    if (ppCB == NULL)
    {
        return E_OUTOFMEMORY;
    }
    return S_OK;
}

STDMETHODIMP SampleGrabberCB::QueryInterface(REFIID riid, void** ppv)
{
    static const QITAB qit[] = 
    {
        QITABENT(SampleGrabberCB, IMFSampleGrabberSinkCallback),
        QITABENT(SampleGrabberCB, IMFClockStateSink),
        { 0 }
    };
    return QISearch(this, qit, riid, ppv);
}

STDMETHODIMP_(ULONG) SampleGrabberCB::AddRef()
{
    return InterlockedIncrement(&m_cRef);
}

STDMETHODIMP_(ULONG) SampleGrabberCB::Release()
{
    ULONG cRef = InterlockedDecrement(&m_cRef);
    if (cRef == 0)
    {
        delete this;
    }
    return cRef;

}

// IMFClockStateSink methods.

// In these example, the IMFClockStateSink methods do not perform any actions. 
// You can use these methods to track the state of the sample grabber sink.

STDMETHODIMP SampleGrabberCB::OnClockStart(MFTIME hnsSystemTime, LONGLONG llClockStartOffset)
{
    return S_OK;
}

STDMETHODIMP SampleGrabberCB::OnClockStop(MFTIME hnsSystemTime)
{
    return S_OK;
}

STDMETHODIMP SampleGrabberCB::OnClockPause(MFTIME hnsSystemTime)
{
    return S_OK;
}

STDMETHODIMP SampleGrabberCB::OnClockRestart(MFTIME hnsSystemTime)
{
    return S_OK;
}

STDMETHODIMP SampleGrabberCB::OnClockSetRate(MFTIME hnsSystemTime, float flRate)
{
    return S_OK;
}

// IMFSampleGrabberSink methods.

STDMETHODIMP SampleGrabberCB::OnSetPresentationClock(IMFPresentationClock* pClock)
{
    return S_OK;
}

STDMETHODIMP SampleGrabberCB::OnProcessSample(REFGUID guidMajorMediaType, DWORD dwSampleFlags,
    LONGLONG llSampleTime, LONGLONG llSampleDuration, const BYTE * pSampleBuffer,
    DWORD dwSampleSize)
{
    // Display information about the sample.
    printf("Sample: start = %I64d, duration = %I64d, bytes = %d\n", llSampleTime, llSampleDuration, dwSampleSize); 
    return S_OK;
}

STDMETHODIMP SampleGrabberCB::OnShutdown()
{
    return S_OK;
}

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