Enumerating Pins
[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 It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation.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.]
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.)
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