The CCCP (Combined Community Codec Pack) is a DirectShow filter pack specifically built for playing anime. It has been assembled by some of the most knowledgeable people in online anime distribution, and one of the primary design goals is to play as much as possible with as little as possible. The CCCP attempts to be as unintrusive on your system as possible. The pack is also now officially endorsed by the Matroska Project, the developers who designed the MKV format.
Software that can be used as an alternative to CCCP (Combined Community Codec Pack):