A codec is a device or program capable of performing encoding and decoding
 on a digital data stream or signal.
The word codec may be a combination of any of the following:
 'COmpressor-DECompressor', 'COder-DECoder', or 'COmpression/DECompression algorithm'.

* DO NOT install more than one CODEC PACK at once !
 (i.e. Combined Community Codec Pack, K-Lite Mega Codec Pack,
 Codec Pack All-in-1, Gordian Knot Codec Pack, etc.)

The consequence is screwing up your video playback
 (includes encoding & decoding), i don't know of anything worse, yet.

I recommend both Gordian Knot Packs if your an Encoder
 or K-Lite Mega Codec Pack if you want to Play any video,
 also Combined Community Codec Pack to Play any video.

You should also, use Google.Com and Wikipedia.Org
 to find out info before you install something.
 I only provide the stuff, sometimes the info,
 but in this case, i provide an archive to the public. ^.^

Freeware Codecs - http://codec.kiev.ua/
K-Lite Homepage - http://www.codecguide.com/
CCCP Homepage - http://www.cccp-project.net/
http://en.wikipedia.org/wiki/Open_source_codecs_and_containers
http://en.wikipedia.org/wiki/K-Lite
http://en.wikipedia.org/wiki/Combined_Community_Codec_Pack