I wanted to trim the possibilities to as low number as possible (even in the "advanced" options). To do this, I basically arbitrarily picked up a few resolution

I wanted to trim the possibilities to as low number as possible (even in the "advanced" options). To do this, I basically arbitrarily picked up a few resolution - iPhone one because that's what iPhone specs are, Flash one because that's YouTube's Flash SD size, and a few others inbetween. The conversion process maintains aspect ratio by setting the larger dimension to what's selected. So for widescreen videos, this would mean that you choose based on the width, and the height will be scaled accordingly. It's not very clear this is how it works tho (it's buried in Video page) - thanks for pointing it out.