>I'm no expert here but as avi file VBR it seems VirtualDub is incompatible.
Nope - as the error msg you encounter suggests, use full processing
mode. This means you have to go to the menus and set vid and audio
compression manually.
It is a pain, but I don't know of another way of working with VBR
avis.
What are you wanting a sample for? It might be that you would be
better off making a contact sheet of thumbs, and should have a look at
Image Grabber.