Better to resize only one dimension?

[tppytel]

I rip lots of SD extras from blurays for my Plex server. I typically deinterlace (if necessary) and resize these to square pixels to avoid any possible problems with less capable Plex clients. At the moment, I've got a bunch of widescreen extras encoded with 472 vertical lines of image and 4 lines of black on the top and bottom. Intuitively, I feel like it would be better to keep those black lines (introducing a little aspect error) and only resize horizontally instead of cropping them and resizing 472 lines to 480 lines. But I'm not sure that intuition is backed up by anything substantial. Any general advice based on experience?

[Asmodian]

Absolutely, preserving native pixels in one dimension noticeably improves quality when re-encoding. Anytime you don't have to resize is good. Do some tests yourself but it is definitely part of the common wisdom.

[tppytel]

Cool, thanks.

[hello_hello]

I hate to say it but I tend to think the common wisdom is somewhat theoretical. I resize the height of DVDs when encoding quite a bit.

Why is there any aspect error though? Assuming there's no cropping and you'd normally resize a DVD to something like 854x480, with 8 lines being cropped from the height, you'd resize to 854x472. Or am I missing something?

If you'd like to try it, and assuming you use Avisynth, this cropping/resizing script has an option called ResizeWO (resize width only). When it's set to true, the script will only crop the height while also applying any specified cropping to the width and resizing it to square pixel dimensions. The ResizeWO option exists because in normal resizing mode the script will sometimes adjust the height cropping to prevent any aspect error and that can cause the height to be "unexpectedly" resized a little. The ResizeWO option prevents the script from resizing the height and hopefully it'd make the process easier. That was it's purpose.

[Q-the-STORM]

Originally Posted by hello_hello

Assuming there's no cropping and you'd normally resize a DVD to something like 854x480, with 8 lines being cropped from the height, you'd resize to 854x472.

I agree with this. Don't resize vertically, but do crop. You only need black lines if you are trying to conform to some standard, like DVD or BD. Since you're playing this on your plex server, there's no need to keep them. You could even encode it on 854x472