http://www.k-litemegacodecpack.com

K-Lite Codec Pack is a collection of codecs, DirectShow filters and tools. Codecs and DirectShow filters are needed for encoding and decoding (playing) audio and video formats. The K-Lite Codec Pack is designed as a user-friendly solution for playing ALL of your movie files. With the K-Lite Codec Pack, your current media player will be able to play all the popular audio and video formats (including mov, rm, mpg, avi, wmv, and flv) and even some rare formats.

Note that K-Lite is a codec pack, not a player, though it does come with a slim version of Windows Media Player Classic (which is really good too).  With the K-Lite Codec Pack, you can uninstall your copy of Quicktime & Real Player, as it can handle even those file types.  Woohoo!

From our experience, K-Lite's Windows Media Player Classic has been able to consistently play every single video file we have thrown at it.  It has had better success than VLC media player (see also), but VLC has other benefits that we will discuss there.  For the best experience, install K-Lite AND VLC, since K-Lite is actually a set of codecs (the Media Player Classic is optional) and will work with VLC, giving it more codec support.

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