Windows Media Player should play .AVI files by default, but a variety of factors from installing other media players to Windows updates can cause them not to play. Here we show you how to fix the problem. See also: How to convert videos to different formats
First, it’s worth pointing out that you can install the free VLC media player which will play virtually every type of video file on a PC. If you’re not bothered about using Windows Media Player, installing VLC is a good idea because it doesn’t require separate codec packs to be installed: it comes with everything you need to play AVI, MKV, MP4, WMV, MPEG-2 and more, and can also stream video from the web.
Update January 2017: In Windows 10, AVI files open with the new Films & TV app. This doesn't support AVI files and you'll see the error below if you try to use it to open one. However, Windows Media Player is still present in Windows 10 and you can search for it in the Start menu. Just drag and drop your AVI file onto the Windows Media Player title bar (or any area where you don't see a circle with a line through it) and it should open and play. As with older versions of Windows, we recommend installing VLC as this handy free video player will play just about every type of video file and it's always useful to have it installed just in case you come across other file types that Windows Media Player won't open.
How to fix AVI playback in Windows Media Player
There are two fairly common reasons why AVI videos stop playing in Windows Media Player (WMP). First is that AVI files are no longer associated with WMP.
To fix this, open WMP and press Alt to show the menu. From the Tools menu choose Options…
In the window that opens, click the File Types tab (note that this doesn’t exist in WMP 12, only in previous versions). Check that Windows video file (.avi) is ticked and, if it isn’t, tick it and click OK.
Another thing to try is updating to the latest version of WMP. Within WMP, press Alt to show the menu if you can’t see it and choose Help, Check for updates… and follow the on-screen instructions.
If this still doesn’t fix the problem you can try installing the K-Lite Codec pack, which includes all the popular video codecs for playing a variety of video formats. Download the Basic pack from codecguide.com.