Import an upright Smartphone Video

Hi,

I'd like to cut a Video wich is 480x848 - so it's upright, but I don't see any option to do that. Always when I import the Video, it's converted to 640x480 with black borders. I can export in 480x848 - but it keeps the black borders. I need a way to create a new preset, or change one of the existing.

pls help

thx