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Enumerating Pins

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Microsoft DirectShow 9.0

Enumerating Pins

Filters support the IBaseFilter::EnumPins method, which enumerates the pins available on the filter. It returns a pointer to the IEnumPins interface. The IEnumPins::Next method retrieves IPin interface pointers.

The following example shows a function that locates a pin with a given direction (input or output) on a given filter. It uses the PIN_DIRECTION enumeration to specify the pin direction, and the IPin::QueryDirection method to find the direction of each enumerated pin. If this function finds a matching pin, it returns an IPin interface pointer with an outstanding reference count. The caller is responsible for releasing the interface.

HRESULT GetPin(IBaseFilter *pFilter, PIN_DIRECTION PinDir, IPin **ppPin)
{
    IEnumPins  *pEnum = NULL;
    IPin       *pPin = NULL;
    HRESULT    hr;

    if (ppPin == NULL)
    {
        return E_POINTER;
    }

    hr = pFilter->EnumPins(&pEnum);
    if (FAILED(hr))
    {
        return hr;
    }
    while(pEnum->Next(1, &pPin, 0) == S_OK)
    {
        PIN_DIRECTION PinDirThis;
        hr = pPin->QueryDirection(&PinDirThis);
        if (FAILED(hr))
        {
            pPin->Release();
            pEnum->Release();
            return hr;
        }
        if (PinDir == PinDirThis)
        {
            // Found a match. Return the IPin pointer to the caller.
            *ppPin = pPin;
            pEnum->Release();
            return S_OK;
        }
        // Release the pin for the next time through the loop.
        pPin->Release();
    }
    // No more pins. We did not find a match.
    pEnum->Release();
    return E_FAIL;  
}

This function could easily be modified to return the nth pin with the specified direction, or the nth unconnected pin. (To find out if a pin is connected to another pin, call the IPin::ConnectedTo method.)

See Also