Most of AVI files are encoded with Xvid, DivX codec, a few are encoded with DX50, AVIV. Installing missing codecs will help Windows Media Player interpret video codec for successful playback.
Method 1. Install missing codecs
1. K-Lite Codec Pack
It comes in a variety of editions from Basic to Mega all of which are free. Originally developed for Kazaa Lite users the K-Lite Codec Pack lets you play practically every video format you might encounter on the Internet in Windows Media Player.
2. Elecard MPEG-4 Codec Pack
This Codec Pack provides a wide range of MPEG-4 decoding/encoding solutions which are offered as DirectShow Filters to enable you to encode and decode various video and audio stream types for playback with Windows Media Player.
3. XVID codec
Then restart your computer and open up your AVI files with Windows Media Player. WMP should now play your AVI files with both audio and video.
Method 2. Transcode AVI to Windows Media Player 12 playable WMV
If you won’t adopt method 1, you can use one top AVI video converter to encode AVI to WMP supported video, this method is easy and quick. Video Converter Ultimate is just the right AVI to Windows Media Player Converter which can convert all kinds of AVI video to Windows Media Player supported video format WMV, AVI, ASF, MPG. Besides converting AVI to WMP video format, it also can transcode AVI, MOV, H.265, DVD, Blu-ray, etc to Windows Media Player for playing. If you are a Mac user, you can read enjoy AVI on Mac OS X 10.11 El Capitan.