AVIS is a
FOURCC which I decided to use to identify video stream in "fake" AVI file wrapping
Avisynth script.
Not every application which can open AVI file can open Avisynth scripts, so you can use
makeAVIS utility to create a "fake" AVI which contains only reference to Avisynth script (or the script itself). When you open this file in application, ffdshow will be used as a video or audio "decompressor" and will deliver frames or audio samples to that application.
This whole idea isn't mine, it was inspired by
Link2 by Videotools.