Transform filters transform the media data that comes into their input pins and send the transformed data out their output pins.

Transform filters can be used in the following ways:

• To compress and decompress data
  
  
• To split audio and visual data
  
  
• To apply effects, such as contrast or warbling, to media data
  
  

DirectShow contains several sample transform filters that perform different kinds of transformations.

This topic steps through the process of creating a transform filter.

It covers five basic steps, and in the last step shows how to override the required member functions in your derived class to implement the transform filter.

It answers two common questions that arise when creating transform filters: Which base class do I use? And how do I override member functions?

The following information is covered in this topic:

• Write a Transform Filter
  
  
• Determine if the Filter Must Copy Media Samples
  
  
• Determine Which Base Classes to Use
  
  
• Instantiate the Filter
  
  
• Make Added Interfaces Available Through NonDelegatingQueryInterface
  
  
• Override the Base Class Member Functions
  
  

For more information, see the following topics:

• Using the CTransformFilter and CTransInPlaceFilter Transform Base Classes
  
  
• Connecting Transform Filters
  
  
• Write a Transform Filter in C/C++