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::CreateInstancefunction. You can also choose to override the CBaseFilter::GetSetupDatamember 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 CTransformFilterclass, you must override the following member functions.

  Function	Purpose
  Transform	Implement transform.
  CheckInputType	Verify support of media type.
  CheckTransform	Verify support for transforming this type (for debugging builds only).
  DecideBufferSize	Set size and count when copying.
  GetMediaType	Suggest media types for the output pin.

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

  Function	Purpose
  Transform	Implement transform.
  CheckInputType	Verify support of media type.

  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 GetPinand GetPinCountmember 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 BreakConnector 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:

  Member function	Reason to override
  NonDelegatingQueryInterface	To distribute any interfaces added in the derived class.
  GetPinCount	If adding more pins to the transform filter.
  GetPin	If adding more pins to the transform filter.
  CheckConnect	To obtain extra interfaces at connect time or for other reasons.
  BreakConnect	To release extra interfaces when connection is broken or for other reasons.
  CompleteConnect	To perform some action at the end of connection (such as reconnecting the input pin).
  SetMediaType	To be notified when the media type has been set.
  StartStreaming	To be notified when entering the streaming state.
  StopStreaming	To be notified when exiting the streaming state.
  AlterQuality	To do anything with quality-control messages other than passing them on.

  
  

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   Last updated on Tuesday, May 18, 2004

  © 2004 Microsoft Corporation. All rights reserved.