What are these Xvid artifacts ?

[Jones_R]

I've done several Xvid encodes, and in all of them I sometimes, during the movie, see an artifact of faint horizontal lines showing near the top of the image. This artifact comes and goes all the time. What is that ?.

I've attached an example. (The image is kind of dark, so turn the brightness on you monitor higher, and you'll see the artifact at the top of the image)

[Acaila]

Please read this (http://forum.doom9.org/forum-rules.htm) page again for attachments.

[Jones_R]

Thanks Acaila.

Here are some more details of what I use for the Xvid encode:
Koepi's 29/12/2002
VirtualDubMod 1.4.13
2 Pass, H.263 (both passes), Bframes -1 (i.e non), Chroma Motion (no other advanced feature selected), 3 CD rip.

[Teegedeck]

Matrix onto _3_ CDs?

[bond]

sorry i dont know why there are horzontal lines, but

Originally posted by Jones_R
Koepi's 29/12/2002try koepis latest build

2 Pass, H.263 (both passes), Bframes -1 (i.e non), Chroma Motion (no other advanced feature selected), 3 CD rip. with this settings you can try getting the movie on 1cd (of course not with ac3) ;)

[Jones_R]

Matrix onto _3_ CDs?
Yeah, I know, kind of an overkill for this movie (even though I use the AC3 track). In the near future I'm going to buy A dvd burner, so I'm letting all my movies be 3 CDs (so I'll be able to fit two movies onto 1 dvd).

I can't believe that even though I use 3 CDs, I still get annoying artifacts like that. :-(

[Jones_R]

with this settings you can try getting the movie on 1cd
Can you suggest a simple encoding change that will make better use with those 3 CDs ?. I mean, I tried to do the most in order to make this Xvid movie as large as possible. I didn't used Bframes, used 2-16 quantizers for both I and P frames. The only things I've left to do (I think) are : 1)lower the max quantizers some more (which I'm not sure will make any quality change in my case), and 2) use MPEG quantization type (but I've read that this can give me more artifacts than I already have, and also, that I have to be an advanced user in order to do it right, which I don't think that I am).

[-h]

Looks like a DCT artifact caused by the fact that you have a black line along the top that you forgot to crop. The same thing happens on DVDs when blocks overlap with the black border.

I couldn't imagine what else it would be.

-h

[Teegedeck]

Jones_R: EDIT: [Bugger, haven't read your posting thoroughly.]But maybe you can spare us all that, install a newer build and test-encode that sequence, again, at quant 2. Be warned though, two-pass is broken on latest XviD builds! But you don't use two-pass anyway, right?;)

[Jones_R]

Teegedeck,
Read again my second post in this thread. What do you mean 2 pass is broken ?, so I can only use 1 pass ?.

-h,
Thanks for the input, I'll try to cut some more from the top.

[bond]

Originally posted by Jones_R
use MPEG quantization type (but I've read that this can give me more artifacts than I already have, and also, that I have to be an advanced user in order to do it right, which I don't think that I am)hm i would at least try mpeg ;)

[Jones_R]

-h,
You were right, it was that top edge "lip" which caused the artifact.
Damn Gordian Knots and its auto crop feature...

Though cropping that "lip" at the top solve the artifact problem, it creates a new problem, since when I crop even the smallest part possible using Gordian Knot, the hight resolution immediately change from 304 pixels to 288 pixels (the big reduction in hight resolution is not proportional to the small reduction in the hight size that I do in order to solve the artifact, so I get a 2.5:1 aspect ratio instead of the original 2.35:1). The only way to solve it (partly) is to reduce the H-Modul to 8 (from 16), but is it healthy to do it ?.

[Jones_R]

Anyone ?.

[seewen]

Just edit the Avisynth script, an set the resize that you want...

[Jones_R]

So simple ?, I wonder why Gordian Knot doesn't let me do this.
Thanks anyway.

[seewen]

But Gordian Knot "let" you do it.. Their's an "edit" button, in the windows where you can choose the Resize method, deinterlace method, etc..

Or you can manually change the Ratio of your movie.. So you don't even need to edit the script

[Teegedeck]

GKnot does this in order to protect you from
a) getting an incorrect aspect ratio - this is not so grave
b) running into trouble by choosing resolutions that aren't dividable by 16 (after resize) - personally, I stick with mulitples of 16, just to be on the safe side, although it's supposed to be no issue with XviD. BTW, multiples of 32 seem to yield marginally better compressiblity

[Jones_R]

But why does Gordian Knot care so much that my output resolution won't be higher than the source (after border cut) ?. Where is the danger with that ?, is it more problematic than dealing with lower output resolution than the source ?.

[Ben Kenobi]

Are you usin ffdshow to decode your video?
I made several Xvid rip, and some have those lines on top, but when i tried to unregister ffdshow filter (regsvr32 /u ffdshow.ax), the lines simply disappear. Lowering postprocessin level also lower lines visibility.

[deXtoRious]

So you're saying basically that it's only there because of the post processing?

[TelemachusMH]

If you want to see if it is post-processing then open the video in vdub, and take a look. If it isn't there then it's not in the video and you know it is the post-processing.

TelemachusMH

[Blight]

I noticed such lines when using one of the DCT-Type setting under FFDShow... try changing the DCT type and see if it makes a difference.

[Ben Kenobi]

Sorry to reup this 3d after so long, but i found a simple workaround for that faint lines. The fault belong to deblocking/deringing filters which adds those lines. To get rid of them, just select "Noise" and set luma noise to 1: it will goes unnoticeable, but there won't be faint lines anymore! ;)