AR after cropping padding

[tominator]

Hi
Im trying to learn the correct way to crop, resize and so on.

I make WMV-streams from DVD-sources. 25fps, 640 width.

So far I think I know that since I want my output to be 640 wide I look at the AR of the source (say 1,78:1) and work out the width by 640/1,78 and round to the closest multiple of 8 which is 360.

This works fine but my issue is this with padding. Sometimes I still have a bit of letterboxing left after the crop and resize which Id like to remove.

How do I remove this without changing the AR even slightly? Do I have to change the size of the output for every extra pixel I crop? Say that I crop 2 pixels off both left and right and 4 pixels off top and bottom. Would this, with a 1,78:1 output, leave me with 636x352 or do I still make the output 640x360? Or should I perhaps change the size of the output but round the numbers to multiples of 8?

Thanks a lot!

[Skelsgard]

Sometimes I still have a bit of letterboxing left after the crop and resize which Id like to remove.

If u´ve cropped and resized, u should have no letterboxing.
When cropping, eliminate anything unnecessary (the letterboxing) no matter what size u end up with. Then, resize this to the final encoding framesize. 2 pixels higher or lower framesize (when your output is 640 x 360) is not gonna really matter to the overall image. Otherwise there´s no way to get exact AR unless u discard actual image or leave unnecessary letterboxing.
Cheers.

[tominator]

Great. Thanks.