How to Crop 1920x1080 (HD) to 640x480 (SD) and Maintain the Aspect Ratio?

[Major Tom MIB]

To get 'full height' SD from HD, do I just crop off 240 pixels from both the left and right sides and resize? Does 1440x1080 HD result in the correct aspect ratio at 640x480 SD? If not, what are the correct cropping values? What if I need to use 720x480, then what cropping values do I use?

640x336 square pixels gives a nice letterboxed display on my player, but I've managed to confuse myself with math :(

Thanks in advance!

[iissmart]

If you want to keep the full picture then you'll need to resize to 856x480, which will keep the 1.78 aspect ratio from the HD video. This is what DVDs do, by stretching the 720x480 (1.5:1) picture to 856x480 when working with anamorphic video to fit on a 16:9 (1.78:1) screen (standard practice).

You could also most certainly crop to 1440x1080 then resize down to 640x480 if you don't care about the picture loss on the left/right side.

[Major Tom MIB]

...856x480..Thanks. Now, I like that--then the dvd player can be set to pan & scan or letterbox. I got that working (somewhat), but I have a limited version dvd encoder and it doesn't offer progressive wide screen film mode (23.xx fps), just 29.97 interlaced or progressive.

[iissmart]

I have heard of very few DVDs actually encoded with 24p video. Most of the time the TV just emulates it by dropping/merging frames from a 30i/p source.

[Kilika_5200]

You might try either TMPGEnc (paid) or SUPER (free) for doing the transcode/resample/resize... SUPER is a little rough around the edges, however I highly recommend TMPGEnc