A codec pack that will give you the ability to play 99% of all the movies that you download from the internet
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.

The K-Lite Codec Pack is a collection of DirectShow filters, VFW/ACM codecs, and tools. Codecs and DirectShow filters are needed for encoding and decoding audio and video formats. The K-Lite Codec Pack is designed as a user-friendly solution for playing all your audio and movie files. With the K-Lite Codec Pack you should be able to play all the popular audio and video formats and even several less common formats.