I'm making VCDs of the Neon Genesis Evangelion series. If anyone knows about these AVIs they come off of, they're very oddly made as far as letterboxes. The problem I'm having is that I use TMPGEnc to edit and cut out unneeded letterboxes, but My images look stretched. I'm wondering what the formula is for calculating how many pixels I need to add or remove from each side.

For example: If I'm editing a video that has a resolution of 352x235 and I want to cut off 8 pixels of the right side. How would I calculate what to change my new resolution to so it won't looked stretched? Also, I have a video with a resolution of 352x235 and I need to edit it to a window of 320x420. How would I successfully change the vertical pixel count to match the new 320 horizontal count?

Please explain in great detail since I'm a little slow.