This site sums it up: “Codec, as a word is an abbreviation of coder/decoder. So, when someone talks about a codec, he or she is talking about two things: coder/encoder plus a decoder. A codec just a coder/encoder combined with a decoder. What’s the relationship between them? Actually, a coder and an encoder are the same thing. Maybe you’ve also heard about codecs, coders, encoders, and decoders, and you’re totally lost. They’re important. Here’s a definition: “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.” The software works on various cases of video file corruption, from broken, choppy and flickering issues to those where videos won't play or show errors.Before moving to the main point, let’s talk about codecs. Consider repairing them with the help of Stellar repair for video. If none of these work, your videos may be corrupted. You can also try restoring Windows to a previous restore point, if the AVI files were opened in the media player before. If AVI videos won't play on Windows 10, change your media player, convert the video file to a different format, or download a codec pack. In order for any AVI video to play on a Windows 10 computer, you need the supported codec.

Now try to play the AVI files in Windows Media Player.

In the system restore window, click Next.You can fix Windows Media Player problem. If the AVI video problem in Windows Media Player has arisen recently and before the videos played, try restoring Windows to an earlier restore point.

How to open avi files on windows