how to play .avi files?

How to play AVI? is probably the most common question a person new to digital video asks. The same question is being asked by many ways: "I downloaded a movie and it wont play", "AVI wont open!" and "This video doesn't work!" -- all of them asking basically the same question. We try to address this question in this article as well as we can.
AVI, video player and codec
Generally speaking, playing an AVI requires two things: a video player software and a codec. Each version of Windows ships with a video player software (called Windows Media Player), so that is not a problem. The problem is called the codec.One of the first terms a digital video freshman gets to know is codec. AVI and codec are inseparable. AVI is simply a file format, that doesn't itself define how the video inside the file was made and how it should be opened. The video inside the AVI is typically a compressed video stream that is made with a special tool, called as encoder [full definition]. Codec, as a word is an abbreviation of Coder / Decoder. The person who put the video inside the video "coded" the video and the person who wants to open the video (that is you..) has to "decode" the video. Codec is a small piece of program that plugs into your computer's operating system and allows the software installed on your computer to perform the "decoding" for the video that has been "coded" with the codec you installed.Therefor, to open the AVI, you need to know how the video was "coded", which means that you need to know what codec you need to use. There are hundreds or thousands of codecs in the world, so it can be an overwhelming task to test them each out individually. Luckily, there are easy ways to get around it..To summarize: it is common that your computer can play some AVIs without any additional software needed and meanwhile refuses to play some AVIs. This is simply due the fact that those AVIs have been compressed using a different codec and your computer has a codec installed already for the ones that work -- and you need to install a new codec to open the one that refuses to play.
The "easiest way"
Despite what stated above about codec and video player software being different things, there are some software packages that wrap both, video player and the most common codecs into one product.As the "easy way", we focus on a free (and open source) video player called VLC. Download VLC from this URL.Simply double-click the downloaded installation package and follow the on-screen instruction to get the software installed and launch it after installation.
Simply go to the File menu and choose Open File from there.
Now, click the Browse button next to the first white line at the top of the window with title "Open.." and navigate through your harddrive for the video you wish to watch and select it.After you have selected the video, click OK and VLC will start playing the video you chose.
VLC should work for approximately 95 percent of the videos from the Internet, specially if they are in .avi format. Obviously there are occassions when you find a video that has been compressed using a codec that is not included within VLC and in those cases, you need to try something else