Find an Interface on a Filter or Pin

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

For many operations in DirectShow, the application calls methods on the Filter Graph Manager. In some situations, however, the application must call a method directly on a filter or pin. For example, many filters expose specialized interfaces that are used to configure the filter.

In the case of a filter interface, you might already have a pointer to the filter's IBaseFilter interface. In that case, simply use QueryInterface to get the other interface. But some filters might be added to the graph by the Filter Graph Manager. (For details, see Intelligent Connect.) In that case, use the IEnumFilters interface to loop through all the filters in the graph, and query each one in turn. The following function demonstrates this:

HRESULT FindFilterInterface(
    IGraphBuilder *pGraph, // Pointer to the Filter Graph Manager.
    REFGUID iid,           // IID of the interface to retrieve.
    void **ppUnk)          // Receives the interface pointer.
{
    if (!pGraph || !ppUnk) return E_POINTER;

    HRESULT hr = E_FAIL;
    IEnumFilters *pEnum = NULL;
    IBaseFilter *pF = NULL;
    if (FAILED(pGraph->EnumFilters(&pEnum)))
    {
        return E_FAIL;
    }
    // Query every filter for the interface.
    while (S_OK == pEnum->Next(1, &pF, 0))
    {
        hr = pF->QueryInterface(iid, ppUnk);
        pF->Release();
        if (SUCCEEDED(hr))
        {
            break;
        }
    }
    pEnum->Release();
    return hr;
}

To find an interface on a pin, use the IEnumPins interface to loop through the pins on a filter. The following function shows how to do this:

HRESULT FindPinInterface(
    IBaseFilter *pFilter,  // Pointer to the filter to search.
    REFGUID iid,           // IID of the interface.
    void **ppUnk)          // Receives the interface pointer.
{
    if (!pFilter || !ppUnk) return E_POINTER;

    HRESULT hr = E_FAIL;
    IEnumPins *pEnum = 0;
    if (FAILED(pFilter->EnumPins(&pEnum)))
    {
        return E_FAIL;
    }
    // Query every pin for the interface.
    IPin *pPin = 0;
    while (S_OK == pEnum->Next(1, &pPin, 0))
    {
        hr = pPin->QueryInterface(iid, ppUnk);
        pPin->Release();
        if (SUCCEEDED(hr))
        {
            break;
        }
    }
    pEnum->Release();
    return hr;
}

The next function searches for an interface on a filter or a pin:

HRESULT FindInterfaceAnywhere(
    IGraphBuilder *pGraph, 
    REFGUID iid, 
    void **ppUnk)
{
    if (!pGraph || !ppUnk) return E_POINTER;
    HRESULT hr = E_FAIL;
    IEnumFilters *pEnum = 0;
    if (FAILED(pGraph->EnumFilters(&pEnum)))
    {
        return E_FAIL;
    }
    // Loop through every filter in the graph.
    IBaseFilter *pF = 0;
    while (S_OK == pEnum->Next(1, &pF, 0))
    {
        hr = pF->QueryInterface(iid, ppUnk);
        if (FAILED(hr))
        {
            // The filter does not expose the interface, but maybe
            // one of its pins does.
            hr = FindPinInterface(pF, iid, ppUnk);
        }
        pF->Release();
        if (SUCCEEDED(hr))
        {
            break;
        }
    }
    pEnum->Release();
    return hr;
}

Note that all of the functions shown here stop at the first successful QueryInterface.

Related topics

Enumerating Filters

Enumerating Pins

ICaptureGraphBuilder2::FindInterface