[MEncoder-users] Normalizing brightness of a video (autolevels filter?)

[Kari Aliranta]

Hello, everyone.

I'm trying to normalize brightness of a bunch of short
videos. The videos are made with a camcorder that
automatically tries to maintain the overall brightness level
  of the picture. However, the videos have a small bright
region that ends up being blocked by people from time to
time: the camcorder tries to adjust and ends up wildly
changing the brightness of the picture all the time. That's
not very nice to look at, so I have question:

Is it possible to somehow automatically normalize the
brightness of a video, so that the dark portions are
brightened and the bright portions are darkened, and the
brightness level stays constant? I tried using the
autolevels filter, but didn't notice any effect. Am I doing
something wrong, does the filter have some prerequisites
that need to filled? Is this kind of normalizing even
theoretically possible?

The exact command script I'm using is the following:

nice -n 19 mencoder $1 -oac copy -ovc xvid -xvidencopts
pass=1 -vf pp=al -o /dev/null && nice -n 19 mencoder $1 -oac
copy -ovc xvid -xvidencopts pass=2:bitrate=1200 -vf pp=al -o
p-$1 && rm divx2*.log

(I also tried entering "-vf pp=al" right after the input
file variable, but it didn't help, either)

Ffmpeg gives the following info about the input file: mjpeg,
yuvj422p, 640x480, 30 tbr, 30 tbn, 30 tbc .

KPA