What the Derived Class Must Provide

The derived filter class must provide a few member functions, typically to:

• Determine if the filter accepts the media type.
• Specify the count and size of any required allocators (for copy transforms only).
• Provide the transform functionality of the filter.

All derived filter classes must implement a static CFactoryTemplate::CreateInstance function. You can also choose to override the CBaseFilter::GetSetupData member function to make your filter self-registering. Beyond this, your classes must override a few member functions in the transform base classes. For more information about instantiating the filter, see Creating a Transform Filter.

If your derived filter class is based on the CTransformFilter class, you must override the following member functions.

If your derived filter class is based on the CTransInPlaceFilter class, override the following member functions.

Beyond providing your transform filter with a default implementation by providing the minimum overrides, you can override other member functions to provide more specialized behavior. Which member functions you override, of course, depends on what you want your filter to do. For example, you must override the CTransformFilter::GetPin and CTransformFilter::GetPinCount member functions if you want to have more than one input pin and one output pin on the filter.

Also, several base class member functions, such as CBasePin::BreakConnect or CBasePin::CompleteConnect, are called as notifications to your filter through the pins. Typically, most of these member functions exist only on the pins. In the classes based on CTransformFilter, the pin functions are implemented to call similarly named functions in the filter class. This means that the member functions you most likely will want to override are all collected into one filter class, so you can leave the pin classes unchanged, making implementation smaller and easier. These member functions are as follows.