DVD->xvid conversion target size way off?

[boosted]

I am trying to convert chapters of my DVD to xvid AVI using Gordian Knot 0.35.0 with a specified file size of 890MB. For some reason, the final file always ends up being 100MB or more too small. Some details of the conversion:
Audio processing disabled, using original .ac3 files muxed afterwards using nandub. 2 tracks.
2 passes, no resizing and no filters other than deinterlace.
I don't know what else I need to provide.

Some chapters come out exactly 890MB after muxing, some come out close, but a couple of them would miss the mark entirely. I did the encoding again, same thing happened. I didn't change the way they're set up between the chapters. Is it because the content of the video just do not require that much space? (lots of static scenes etc) What am I doing wrong?

any help would be appreciated,
-boosted
ps. I tried searching but due to the nature of the problem, it's hard to specify a search parameter that will return the thread that I want.

[celtic_druid]

Are your quants capped at all? Also what build of XviD?
Sounds to me that you just saturated the codec. You could check though by looking at the average quant. If you have the quants capped at 2 then you can't have a 2nd pass larger than the first. So those chapters that are more compressable will be undersized.

[boosted]

Thank you for replying to help celtic_druid. I'm using XviD-1.1.0-Beta2-04042005 I followed the GKnot ILLUSTRATED GUIDE (MPEG2toAVI) v.3, which did have a section that asked me to change the min I-frame and P-frame to 2, but I have no idea what that means. Max I-frame P-frame and B-frame are at 31.

So you're saying the undersized files are a result of the content being more compressible? Not a result of higher compression? (less quality) In another words, the file is as big as Xvid can get?

-boosted

[Baldrick]

please post dvd to avi in the dvd to avi forum. moving you.

[boosted]

I thought I was posting in the newbie conversion forum. Since this is a pretty newbie question.

[celtic_druid]

Yep, as big as XviD can get. That is without quant 1's (some would call that padding), a higher resolution or a higher quality quant matrix.

[boosted]

Wow I didn't know the size can vary that much. 25% The quality seems to be about the same as the bigger files. And the chapter are mostly non-moving scenes. I guess that's the reason.

What would changing quant to 1 do?

[celtic_druid]

The smaller the quant the larger (in size) it is. If you set the 2nd pass to be larger than the first (which is run by default at constant quant 2) then XviD will (if they aren't capped) insert quant 1's to try and hit the desired size. Problem is that you may then get oversized encodes with the default overflow settings as too many quant 1's are inserted.

As I said above, some people would say that using quant 1's is just padding and that the quality is no better.

What quant matrix are you using? Because as I said if you want larger encodes, you can always try a higher quality matrix.

[boosted]

I have no idea what quant matrix I'm using. It should be default since I didn't change any numbers in the matrix. Quantization type is set at H.263 if that makes a difference. Sorry I just have no idea what it means.

[celtic_druid]

It means that you could use a higher quality quant matrix. For a start you could use MPEG. This should give you a sharp image. You could also try an custom one like one of sharktooth's.

[boosted]

Thank you for your continued assistance celtic_druid. Where can I find the sharktooth matrix? I googled sharktooth matrix and it returned some sharktooth fossil links lol. Maybe you can point me to some page where I can learn how it works and how it affects the quality so I don't have to keep bugging you.
Also, when you say mpeg, do you mean mpeg2 or mpeg4?

[celtic_druid]

http://forum.doom9.org/showthread.php?s=&threadid=83125

[boosted]

Thanks. I will give mpeg and custom matrix a try

[boosted]

Are these matrix suppsed to be loaded into both the first pass and 2nd pass of the configuration?

[boosted]

Just tried encoding the same chapter using mpeg, then mpeg-custom using the ultra high bitrate matrix, (loaded the matrix for both passes) the 2 files came out to be the exact same size. They quality seems to be identical too. Any idea why that is? I'm doing a third encode using mpeg-custom and high bitrate matrix.
Upon closer inspection, it seems that my xvid codec configuration is different than the GK xvid. IS that even possible?

[celtic_druid]

Check the files with MPEG4Modifier to varify the matrix used. You could also run a simple FC on them, because it sounds to me like the matrix isn't actually being used if they are the exact same size.

and yes you need to use it for both passes.

[boosted]

You were right, for some reason, the matrix wasn't used. I did the encode again last night and checked it with MPEG4Modifier and it showed the custom matrix on my second try. Weird. I couldn't really tell much difference from the encodes, but MPEG, whether custom or default, showed a slight sharpen look. I guess there's a point of diminishing return.

Thank you again celtic_druid for your patience. I got one last thing, I also Divx Pro 5.2.1 installed. For some reason, both divx and xvid encodes are being played back by the divx decoder. I tried reinstalling xvid and asked it to playback all mpeg4 file types, it didn't make any difference. I guess the short answer would be to reinstall Divx?

[celtic_druid]

Can't really think of any reason to have DivX installed. Go into the DivX decoder config and disable generic MPEG-4 support. It will no longer decode XviD.

[boosted]

Well duh! I should have thought of that. lol If Xvid has that option, so should Divx. How could I have missed it. Thanks.