Set the wav file aside for a moment…you’ll use it in ffmeggui.
Import your original avi file into TMPGenc Plus and convert the avi to mpeg, but just output the video stream. To do this, you hit ES Video only in the options.
If for some bizarre reason it won’t let you do this, just encode normally to mpeg as you did in the beginning, then demux this mpeg file using the mpeg tools in TMPGenc. This will give you an m2v file and a bad audio stream that you can discard.