CCCP (Combined Community Codec Pack) is a DirectShow filter pack, it is a filter pack specifically built for playing anime. It has been assembled by some of the most knowledgeable people in the anime world, and one of the primary design goals is to play as much possible with as little as possible. It attempts to be as unintrusive on your system as possible.
Jokes aside, the CCCP was created to replace the filter packs provided by several anime fansub groups into a single reliable pack capable of decoding practically any group's files - without breaking compatibility for other formats. Since then we've grown into a pack that can decode more or less anything that you will run into during your travels on the internet.

Supported Formats include:
Containers:
* AVI (multiple audio streams and softsubs work too)
* MKV (Matroska)
* OGM & Ogg
* MP4
* TS (MPEG Transport Stream)
* FLV

Video codecs:
* MPEG1 is supported by Windows
* MPEG2
* MPEG4-ASP
* Xvid
* DivX (all versions)
* Generic/other MPEG4 ASP (3ivx, lavc etc.)
* MPEG-4 AVC/H.264
* Theora
* WMV9
* Flash Video

Audio codecs:
* MP3 and MP2 and MP1
* AC3
* DTS
* AAC
* Vorbis
* IMA ADPCM - rare
* LPCM - on some DVDs, more common on HD DV & BD
* FLAC - no .flac splitter included, you can only play it if it's in MKV
* TTA
* WavPack

Players: Anything that is basically sane and uses DirectShow.

The license of this software is Freeware, you can free download and free use this codec pack software.