Resizing - what to round off to?

[xycer]

ive seen many people round off to different numbers. Ive even seen some people round off to the nearest divisible number of 4.

do i just round off to the nearest number? ie if the new resized height calculates to 269.5, set it to 270 and if its 269.4, set it to 269.

[manono]

Hi-

What's this for? AVI?

If so, MPEG-4 compression works on macroblocks of 16. Therefore, for compressibility reasons, it's usually recommended to resize no smaller than Mod16 (divisible by 16). A case can even be made for compressing by Mod32 (even better compression, although you'll lose a lot of resolutions). But Mod16 is generally recommended.

For both compression and compatability reasons you shouldn't resize below Mod16. Some video cards (old Matrox cards, for example) play Mod8 funny.

Having said that, if your card plays Mods 8 and 4 OK, and you don't care about the compression gains, I guess you can go ahead and use them, but if anyone else sees it, they might laugh at your incompetence . I know I would. Under no circumstances use Mods 2 or 1.

[xycer]

so the resized vertical should be divisible by 16?!?! thats a pretty specific number isnt it? (not many numbers are divisible by 16).

wow, theres a lot i have to learn about resizing than i thought. Maybe i should just use TMPGEnc's auto resizing feature (full screen keep aspect ratio). Would the quality be better if you resized it with say lanczos vs letting TMPGEnc auto resize it for you? I understand the different resizing options (like lanczos, bicubic etc) makes things more or less sharp right?

[manono]

Hi-

Sorry, but I know nothing about encoding with TMPGEnc. I use VDubMod. TMPGEnc is much slower for DVD->AVI encoding as it requires RGB input. However, if the source is a DVD, I don't see how keeping the aspect ratio is going to be good, as the AR has to be changed from 16:9 or 4:3 to 1:1 for AVI. But it's very possible that I just don't understand that setting.

I usually use Lanczos. A lot of people here use Lanczos4. I have no idea what resizer TMPGEnc uses in the Auto setting. Maybe someone else can help.

[xycer]

im talking about AVI/Divx/Xvid to DVD MPEG2 converting if that makes a difference. What i usually do is resize with Virtualdub, frameserve it to TMPGEnc to convert to MPEG2 DVD. Then i use TMPGEnc DVD Author to convert to DVD format.

no offense but telling me that the resized vertical has to be divisible by 16 is still hard to believe. For example, i was told by a few people that the correct formula for resizing to DVD format is this (for 16:9 DAR):
852 / sources width = * by the sources height.
for example, i have an AVI that is 576x240. So i would go:
852/576 = 1.479167 * 240 = 355. Now the closest number that is divisible by 16 is 352 so is that what i would have to resize it to?

about the resizing options, the only lanczos option vdub has is lanczos3, so i use that. I'm curious if the quality resizing with lanczos is better than letting TMPGEnc resize it for you.

[manono]

My very first sentence in my first post asked what your output format was to be. You didn't answer, so I assumed I was correct in thinking it was for AVI. Since it's not, then just use FitCD for generating scripts if you use AviSynth. If not, then use TMPGEnc's settings. This is the first time you've actually said it's for DVD. Of course that changes everything. I'm done.

[xycer]

lol, by AVI, i thought you meant DEALING with AVI, not converting to... sorry for not answering, i just thought we were on the same page.

anyway, what about that whole divisible by 16 thing? is my formula right? if the resized video turns out to be like 355.45, do i just round to the nearest 10th?

from what ive been told, the proper resize formulas are:

for 16:9 DAR: 852 / source width = * source height = resized height and add borders to fit 480 so its 852x480

for 4:3 DAR: 720 / source width = * source height = resized height and add borders to fit 480 so its 720x480

im also kind of confused about 16:9 DVD's. are they 852x480 or 853x480?

[absinthecarolinas]

Read this page. Then read it again. If you don't completely understand it, read it again.

Take your time. Read it slowly.

Once you do understand it, read it again!

I once spent most of a day reading that page over and over. Once it clicks, it's like a ray of sunshine 8)

-abs

P.S. Don't start your project until you read the page. ALL NTSC DVDs will be 720x480 (or maybe 352x480, if you want half-D1 rez). If that doesn't make sense to you right now ... see above!

[junkmalle]

MPEG2 and MPEG4 codecs start by breaking an image up into 16x16 pixel blocks. Each block is then encoded separately. If the width or height of the image is not a multiple of 16 the encoder/decoder will have to pad the edges to complete the 16x16 blocks (or at least spend additional time being carfull about how it handles the edge blocks). So you get slightly better encoding if the width and height are multiples of 16.

Beyond that, some codecs have specific requirements about the width and height. Many don't allow odd values, some require multiples of 2 or 4. And the restrictions may be different for width and height.