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Pins provide enumerators to enable other objects to determine the pin's media type. A pin provides the media type enumerator (the IEnumMediaTypesinterface), which the pin base classes implement to call the GetMediaTypemember function in the pin class. In the copy transform filter classes, each pin's CTransformOutputPin::GetMediaTypemember function simply calls the virtual CTransformFilter::GetMediaTypemember function in the filter class. Your derived class must implement this member function to provide each supported media type in a list of media types.
In the transform-inplace classes, the enumerators form a transparent channel between the filters upstream and downstream from the transform filter. If the transform filter's input pin must perform an enumeration, it obtains an enumerator from the downstream filter's input pin. If the output pin must perform an enumeration, it obtains an enumerator from the upstream filter's output pin. One consequence of this is that transform-inplace filters can't connect to each other unless at least one of them is connected to something else, because neither of the transform-inplace filters can propose any media type for the connection.
Last updated on Tuesday, May 18, 2004