[MPlayer-dev-eng] [PATCH] fix for ve_xvid4 fixed quantizer mode problem

[Michael Neuhauser]

Hi, all!

Fixed quantizer mode does not work properly with the XviD 1.0 export
module libmpcodecs/xvid4.c: With the command

  mencoder in.vob -o out.avi -oac copy -endpos 10 -ovc xvid \
    -xvidencopts fixed_quant=2:psnr

(i.e. encode 10 secs with xvid at a fixed quantizer of 2 and generate
psnr stats), the following quantizer histograms can be obtained from the
psnr_* files:

original mencoder (cvs HEAD of 2004-07-13)

 Q     #
 1    48 (20.3%) ************
 2    70 (29.7%) ******************
 3    86 (36.4%) **********************
 4    32 (13.6%) ********

cvs-mencoder + attached patch

 2    82 (34.7%) *********************
 4   154 (65.3%) ****************************************

The latter being correct (q=4 values because of B-frames). 
 
An inspection of libmpcodecs/xvid4.c and
xvidcore-1.0.1/src/plugins/plugin_single.c:rc_single_before() revealed
that the fixed quantizer zone parameters base & increment are set to 1/q
instead of q (for fixed_quant == q) in set_create_struct() (i.e. base
has to be set to the denominator of q, not the numerator as it is done
in cvs).

Regards,
	Mike
-- 
Dr. Michael Neuhauser                phone: +43 1 789 08 49 - 30
Firmix Software GmbH                   fax: +43 1 789 08 49 - 55
Vienna/Austria/Europe                      email: mike at firmix.at
Embedded Linux Development and Services    http://www.firmix.at/
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