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Creating Transform Nodes

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A transform node represents a Media Foundation transform (MFT), such as a decoder or encoder. There are several different ways to initialize a transform node:

  • From a pointer to the MFT.
  • From a CLSID for the MFT.
  • From a pointer to an activation object for the MFT.

If you are going to load the topology inside the protected media path (PMP), you must use either the CLSID or an activation object, so that the MFT can be created inside the protected process. The first approach (using a pointer to the MFT) does not work with the PMP.

Creating a Transform Node from an MFT

To create a transform node from an MFT, do the following:

  1. Create an instance of the MFT and get a pointer to the IMFTransform interface of the MFT.
  2. Call MFCreateTopologyNode with the MF_TOPOLOGY_TRANSFORM_NODE flag to create the transform node.
  3. Call IMFTopologyNode::SetObject and pass in the IMFTransform pointer.
  4. Call IMFTopology::AddNode to add the node to the topology.

The following example creates and initializes a transform node from an MFT.

HRESULT AddTransformNode(
    IMFTopology *pTopology,     // Topology.
    IMFTransform *pMFT,         // MFT.
    IMFTopologyNode **ppNode    // Receives the node pointer.
    )
{
    *ppNode = NULL;

    IMFTopologyNode *pNode = NULL;
    
    // Create the node.
    HRESULT hr = MFCreateTopologyNode(MF_TOPOLOGY_TRANSFORM_NODE, &pNode);

    // Set the object pointer.
    if (SUCCEEDED(hr))
    {
        hr = pNode->SetObject(pMFT);
    }

    // Add the node to the topology.
    if (SUCCEEDED(hr))
    {
        hr = pTopology->AddNode(pNode);
    }

    // Return the pointer to the caller.
    if (SUCCEEDED(hr))
    {
        *ppNode = pNode;
        (*ppNode)->AddRef();
    }

    SafeRelease(&pNode);
    return hr;
}

Creating a Transform Node from a CLSID

To create a transform node from a CLSID, do the following:

  1. Find the CLSID of the MFT. You can use the MFTEnum function to find the CLSIDs of MFTs by category, such as decoders or encoders. You might also know the CLSID of a particular MFT that you want to use (for example, if you implemented your own custom MFT).
  2. Call MFCreateTopologyNode with the MF_TOPOLOGY_TRANSFORM_NODE flag to create the transform node.
  3. Set the MF_TOPONODE_TRANSFORM_OBJECTID attribute on the node. The attribute value is the CLSID.
  4. Call IMFTopology::AddNode to add the node to the topology.

The following example creates and initializes a transform node from a CLSID.

HRESULT AddTransformNode(
    IMFTopology *pTopology,     // Topology.
    const CLSID& clsid,         // CLSID of the MFT.
    IMFTopologyNode **ppNode    // Receives the node pointer.
    )
{
    *ppNode = NULL;

    IMFTopologyNode *pNode = NULL;
    
    // Create the node.
    HRESULT hr = MFCreateTopologyNode(MF_TOPOLOGY_TRANSFORM_NODE, &pNode);

    // Set the CLSID attribute.

    if (SUCCEEDED(hr))
    {
        hr = pNode->SetGUID(MF_TOPONODE_TRANSFORM_OBJECTID, clsid);
    }

    // Add the node to the topology.
    if (SUCCEEDED(hr))
    {
        hr = pTopology->AddNode(pNode);
    }

    // Return the pointer to the caller.
    if (SUCCEEDED(hr))
    {
        *ppNode = pNode;
        (*ppNode)->AddRef();
    }

    SafeRelease(&pNode);
    return hr;
}

Creating a Transform Node from an Activation Object

Some MFTs provide activation objects. For example, the MFCreateWMAEncoderActivate function returns an activation object for the Windows Media Audio (WMA) encoder. The exact function depends on the MFT. Not every MFT provides an activation object. For more information, see Activation Objects.

You can also get an MFT activation object by calling the MFTEnumEx function.

To create a transform node from an activation object, do the following:

  1. Create the activation object and get a pointer to the IMFActivate interface of the activation object.
  2. Call MFCreateTopologyNode with the MF_TOPOLOGY_TRANSFORM_NODE flag to create the transform node.
  3. Call IMFTopologyNode::SetObject and pass in the IMFActivate pointer.
  4. Call IMFTopology::AddNode to add the node to the topology.

The following example creates and initializes a transform node from an activation object.

HRESULT AddTransformNode(
    IMFTopology *pTopology,     // Topology.
    IMFActivate *pActivate,     // MFT activation object.
    IMFTopologyNode **ppNode    // Receives the node pointer.
    )
{
    *ppNode = NULL;

    IMFTopologyNode *pNode = NULL;
    
    // Create the node.
    HRESULT hr = MFCreateTopologyNode(MF_TOPOLOGY_TRANSFORM_NODE, &pNode);

    // Set the object pointer.
    if (SUCCEEDED(hr))
    {
        hr = pNode->SetObject(pActivate);
    }

    // Add the node to the topology.
    if (SUCCEEDED(hr))
    {
        hr = pTopology->AddNode(pNode);
    }

    // Return the pointer to the caller.
    if (SUCCEEDED(hr))
    {
        *ppNode = pNode;
        (*ppNode)->AddRef();
    }

    SafeRelease(&pNode);
    return hr;
}

Creating Topologies

Topologies

IMFTopologyNode