The K-Lite Codec Pack is a collection of various DirectShow filters, codecs, and tools for video playback and encoding.
Why you should use CCCP instead of K-Lite
K-Lite Codec Pack comes in several different flavours. From basic (small) to mega (large). Most people use the larger versions of the pack. These packs install a LOT of things. Most of which you probably don't need. The more codecs and filters you have installed on your computer, the more likely they will conflict.
CCCP has been designed as a small, yet powerful pack, for playback only. It allows you to play all common audio and video formats that are used in and outside the anime scene.