K-Lite Codec Pack is a collection of codecs and related tools. Codec is short for Compressor-decompressor. Codecs are needed for encoding and decoding (playing) audio and video. It is designed as a user-friendly solution for playing all your movie files. You should be able to play 99% of all the movies that you download from the Internet.
ftp://ftp.ku.lt/pub/Windows/audio/K-Lite/klcodec231f.exe