KMPlayer handles both audio and video, and supports a wide range of different formats, meaning that once installed, you should never need to touch another player. Video playback is particularly impressive thanks to the range of processing tools available that allow you to sharpen, change picture properties, apply filters and even make video captures from within the program.
K-Lite Codec Pack
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.
VLC Media Player
VLC is a free and open source cross-platform multimedia player and framework that plays most multimedia files as well as DVD, Audio CD, VCD, and various streaming protocols.