Cropping math?

[Kban]

My TV overscans a lot and testing different sizes I found out with an anime episode with 640x480 resolution that if I converted it to SVCD at 450x450 I can be able to see the whole video.

Now I want to convert a 640x352 widescreen movie to SVCD, but if I use center(custom size) and use 450x450 the image will be full screen and I want to keep it widescreen. What size should I choose knowing for this widescreen movie knowing that for 4:3 size movies I need to use 450x450 instead of 480x480 to avoid overscanning?

[Kban]

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