divisible by (4,8,16) ?

[russofris]

Good evening,

I am in the process of encoding some TV caps with XVid. The overscan on my Hauppauge is a little off, so I have to crop 8 pixels off of X1 (the left) using VDub's (Latest vdubmod) null transform. This leaves me at 712x480. Using XviD-22032003-1.

Easy question. Having searched the forum for the word "Divisible", I came accross a number of posts that stated that the dimentions must be divisible by 16. Some posts said 8, some posts said 4... This conflicting information leaves me a little confused. At 712x480, I am not seeing any visible defects when playing back through wmplayer (no ffdshow or anything installed).

Is there some hidden advantage in going with resolutions divisible by 16? Does this apply to both vertical and horizontal resolutions?

Thank you for your time,
Frank Russo

[manono]

Hi and welcome to the forum-

Compression is better when using Mod 16 resolutions. And some older video cards can't handle Mod 8 or less. For more information, please see This (http://forum.doom9.org/showthread.php?s=&threadid=42708) (about a foot and a half down from the top). But having said that, if you don't care about losing a few per cent in compressibility, and your vid card handles Mod 8 resolutions, then no big deal.

[kastro68]

Does mod 32 still work best? Although mod 16 can be a subset of mod 32.

I remember someone doing some comparisons a looooooooooooooooooooooooong time ago and came up with the conclusion that mod 32 has better compression.

To this day I still use mod 32 at the expense of the aspect ratio.

[manono]

Hi-

Does mod 32 still work best?

Yes, and I mention that fact in the sticky to which I linked. Personally I use the Width=Mod 32 and Height=Mod 16 of GKnot because more resolutions are available that way than if both are Mod 32. But since russofris was asking specifically about Mods 16, 8, and 4, I addressed my answer to that. To each his own though, but for best compressibility, Mod 32 is the way to go.

[jarthel]

let's say I have the following script
------------
mpeg2source(...........)
crop(8,8,704,464)
#telecide/decimate here
#some smoothing here
lanczosresize(640,480)
---------------

Would you say my encode is mod4, 8, 6 or 32? as all the options apply to it.

Thanks

Jayel

[Blight]

jarthel:
Width = Mod 128
Height = Mod 32

If 640 divided by 128 is EXACTLY 5.0 and not 5.00001 then you can say it's "mod 128".

Since 480 divided by 64 is 7.5 ... the .5 means it's not MOD 64 ... but 480 divided by 32 is 15.0 so it is MOD 32... Get it?

[jarthel]

Ok. I get it now. Thank you. :)

Jayel