MSDN Article on how to write a WIC CODEC
Peggi, Lead PM on WIC, put together a most excellent write up for all of the things that go into writing a CODEC for WIC. It covers everything from the required interfaces that need to be implemented to which registry keys are required. The article is now up on MSDN. Check it out here!
If anyone has anyone has feedback on the whitepaper, please send mail to codecs@microsoft.com.