reencoding to 480x480 without resizing

[cicada]

i have a bunch of videos of different resolutions in my computer, and i want to convert them all to svcd 480x480 mpg, but when i do this they resize and get blocky, is there any way to keep the video resolution and just add black bars to make it 480x480?
Thanx

[Shabubu]

Avisynth and vdub have an add borders function that can do that, then frameserve out to TMPGenc. Guides can be found at doom9.net. The avisynth script goes something like this

BicubicResize(480,335,0.333,0.333)
AddBorders(0,121,0,120)