How to Set the Playback Stop Time

This topic describes how to set a stop time for playback when using the Media Session.

Setting the Stop Time Before Playback Begins

Before you queue a topology for playback, you can specify the stop time by using the MF_TOPONODE_MEDIASTOP attribute. For each output node in the topology, set the value of the MF_TOPONODE_MEDIASTOP to the stop time in 100-nanosecond units.

Note that setting this attribute after playback starts has no effect. Therefore, set the attribute before calling IMFMediaSession::Start.

The following code shows how to set the stop time on an existing topology.


template <class Q>
HRESULT GetCollectionObject(IMFCollection *pCollection, DWORD dwIndex, Q **ppObject)
{
    *ppObject = NULL;   // zero output

    IUnknown *pUnk = NULL;
    HRESULT hr = pCollection->GetElement(dwIndex, &pUnk);
    if (SUCCEEDED(hr))
    {
        hr = pUnk->QueryInterface(IID_PPV_ARGS(ppObject));
        pUnk->Release();
    }
    return hr;
}

HRESULT SetMediaStop(IMFTopology *pTopology, const LONGLONG& stop)
{
    IMFCollection *pCol = NULL;
    DWORD cNodes;

    HRESULT hr = pTopology->GetSourceNodeCollection(&pCol);
    if (SUCCEEDED(hr))
    {
        hr = pCol->GetElementCount(&cNodes);
    }
    if (SUCCEEDED(hr))
    {
        for (DWORD i = 0; i < cNodes; i++)
        {
            IMFTopologyNode *pNode;
            hr = GetCollectionObject(pCol, i, &pNode);
            if (SUCCEEDED(hr))
            {
                pNode->SetUINT64(MF_TOPONODE_MEDIASTOP, stop);
            }
            pNode->Release();
        }
    }
    SafeRelease(&pCol);
    return hr;
}


Setting the Stop Time After Playback Has Started

There is a way to set the stop time after the Media Session starts playback, by using the IMFTopologyNodeAttributeEditor interface.

Important   This interface has a serious limitation, because the stop time is specified as a 32-bit value. That means the maximum stop time that you can set using this interface is 0xFFFFFFFF, or just over 7 minutes. This limitation is due to an incorrect structure definition.

To set the stop time using the IMFTopologyNodeAttributeEditor interface, perform the following steps.

  1. Call MFGetService to get the IMFTopologyNodeAttributeEditor interface from the Media Session.
  2. Call IMFTopology::GetTopologyID to get the ID of the playback topology.
  3. For each output node in the topology, call IMFTopologyNodeAttributeEditor::UpdateNodeAttributes. This method takes the topology ID and a pointer to a MFTOPONODE_ATTRIBUTE_UPDATE structure. Initialize the structure as follows.
    MemberValue
    NodeIdThe node ID. To get the node ID, call call IMFTopologyNode::GetTopoNodeID.
    guidAttributeKeyMF_TOPONODE_MEDIASTOP
    attrTypeMF_ATTRIBUTE_UINT64
    u64The stop time, in 100-nanosecond units.

     

Be careful to set the value of attrType correctly. Although u64 is a 32-bit type, the method requires that attrType be set to MF_ATTRIBUTE_UINT64.

The following code shows these steps.


HRESULT SetMediaStopDynamic(IMFMediaSession *pSession, IMFTopology *pTopology, const LONGLONG& stop)
{
    if (stop > MAXUINT32)
    {
        return E_INVALIDARG;
    }

    IMFTopologyNodeAttributeEditor *pAttr = NULL;
    IMFCollection *pCol = NULL;
    IMFTopologyNode *pNode = NULL;

    HRESULT hr = MFGetService(pSession, MF_TOPONODE_ATTRIBUTE_EDITOR_SERVICE, IID_PPV_ARGS(&pAttr));
    if (FAILED(hr))
    {
        goto done;
    }

    TOPOID id;
    hr = pTopology->GetTopologyID(&id);
    if (FAILED(hr))
    {
        goto done;
    }

    DWORD cNodes;
    hr = pTopology->GetSourceNodeCollection(&pCol);
    if (FAILED(hr))
    {
        goto done;
    }

    hr = pCol->GetElementCount(&cNodes);
    if (FAILED(hr))
    {
        goto done;
    }

    for (DWORD i = 0; i < cNodes; i++)
    {
        IMFTopologyNode *pNode;
        hr = GetCollectionObject(pCol, i, &pNode);
        if (FAILED(hr))
        {
            goto done;
        }

        TOPOID nodeID;
        hr = pNode->GetTopoNodeID(&nodeID);
        if (FAILED(hr))
        {
            goto done;
        }

        MFTOPONODE_ATTRIBUTE_UPDATE update;
        update.NodeId = nodeID;
        update.guidAttributeKey = MF_TOPONODE_MEDIASTOP;
        update.attrType = MF_ATTRIBUTE_UINT64;
        update.u64 = (UINT32)stop;

        hr = pAttr->UpdateNodeAttributes(id, 1, &update);
        if (FAILED(hr))
        {
            goto done;
        }
        SafeRelease(&pNode);
    }

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


 

 

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