Curve compresion dude

[locura]

Hi, I have realised some compression tests with "Crimson Tide" film with different configurations in the compression curves.

General Data:

LumaFilter()
Crop(4,76,-4,-76)
Undot()
BicubicResize(640,256,0,0.75)

XVID KOEPI 14-5-2003
File size = 540000kb

Bframes = off
Vhq = off
chome motion = off
trellis quant = off
Iframe-max = 2
Iframe-min = 4
Pframe max = 2
Pframe min = 10

Other parameters have default value and without compressing the credits.

First test - VBR:

High bitrate scenes = 0
Low bitrate scenes = 0
Bitrate payback delayframes = 250
Payback proportionality = active
Alternative curve = off

Second test - Curve compression

High bitrate scenes = 100
Low bitrate scenes = 100
Bitrate payback delayframes = 1
Payback proportionality = active
Alternative curve = off

Third test - Curve compresion

High bitrate scenes = 25
Low bitrate scenes = 25
Bitrate payback delayframes = 300
Payback proportionality = active
Alternative curve = off

In these test, and most in lower videos, the second test gives a better result, avoiding macroblocks in the movement scenes.

Because, I asked me how really works the compression curve to give these results, because the quality has not worsened in any moment, just the opposite, it has improved; but really with this configuration it is supposed that the bitrate allotment is more limited, for what in theory the quality should be smaller.

Regards, Affar

PD: Sorry for my poor english, but I am Spanish

[Mashabak]

Hi, one question:

About this topic, I understand that the alternative curve works around a relative minimum quality. But, keeping in mind that and that, for example, the strength determines the grade of importance of the size wanted by us in the calculate of this minimum quality, I want to know which would be really the method that uses the codec to calculate that value. That is to say: What factors act and in that way so that xvid determines which is the relative minimum quality and the stocking of bitrate of the frames?

Regards.

[Teegedeck]

Perhaps you'll find some useful explanations by Foxer in this thread (http://forum.doom9.org/showthread.php?&threadid=21228&highlight=minimum+quality).