What is a .avi file?

You found an AVI file in an old folder, a backup drive, or a security camera system. It still works. AVI (Audio Video Interleave) was introduced by Microsoft in 1992, and while the format hasn't been a sensible choice for new video in over a decade, existing AVI files aren't going anywhere.

AVI works by interleaving audio and video data in alternating chunks — clever for 1992, but it lacks features the modern world expects: no native streaming support, no variable frame rates, no efficient metadata handling. AVI files tend to be enormous because many of them use older codecs or minimal compression. You'll encounter them in old video archives, security camera footage, downloaded movies from the mid-2000s, and any system that hasn't been updated in fifteen years.

VLC plays AVI files without complaint. Windows Media Player handles most of them. For anything new, MP4 is better in every measurable way. Converting old AVI files to MP4 with fwip preserves the content while dramatically reducing file size and adding modern compatibility.