It's simple although your gonna need a few things first. This is for Windows machines only.
You need to get:
-First close GIMP.
-You'll need to download these then install GIMP GAP.
-Then you'll need to extract UC-AVI and then place the
application file (not the folder) into:
This folder should contain other application files (plug-ins).
Once you have installed GIMP GAP and moved the UC-AVI application
plug-in to the plug-in folders you'll need to restart GIMP.
You should now be able to open avi. files.
*However the avi. files need to be uncompressed so you'll need to
a converter program to make a compressed avi. to uncompressed.
Also remember that GIMP cuts the avi. down to each frame so if you
got more than about 10 seconds you've got a lot of frames to edit.
Hope this helps everyone that had problems with the avi plug-ins.
Another thing is that some articles said to put the uc-avi in:
Which did not work for me.