Dealing with Aspect Ratio

From Zanecorpwiki

First off, there are two aspect ratios to any video source. The 'display aspect ratio' (DAR) and the pixel aspect ratio (PAR). When people say aspect ratio they almost always mean the DAR.

DVD players generally will look at the source pixel size and the DAR and set up PAR correctly. When transcoding, this isn't always the case. I believe the most common cause (in say, going from a DVD VOB to a xvid4 AVI) that the DAR is not encoded as it would be on the DVD, so unless you tell the player the aspect ratio, it will assume a PAR of 1:1 (square pixels) and you'll get either a squished or stretched image.

For example, a 720x480 pixel, 16:9 DAR has a PAR of 256:216, meaning the pixels are rectangular and slightly longer than they are tall. To correct for this, we have to resize resulting image to maintain the DAR. If we wanted to keep a high resolution, then 720x406 works. (405 is actually closer, but the number has to be even).

transcode ... --import_asr 3 --export_asr 3 -Z 720x406 ...

Not 100% sure if the two ASR option (aspect ratio) are necessary, but they don't hurt. 3 = 16:9 (1.78), BTW. The Z option resizes the image.