xine, mPlayer or Kaffeine brightness ?
 

Running Fedora FC4 KDE - installed from yum xine, mplayer and Kaffeine. In Xine cannot adjust brightness and it seems to be running Xv. Kgamma will only adjust screen background not the video window. Although I'm running it on an ancient machine (PII 450 with 16MB TNT) video is pretty smooth and totally watchable but the contrast/brightness settings are too dark. If I run in opengl mode can adjust but loose audio sync although video is pretty smooth. Any ideas how to set brightness when under Xv?

http://mplayerhq.hu/DOCS/HTML/en/index.html
http://mplayerhq.hu/DOCS/man/en/mplayer.1.html

Here is for Mplayer, not sure what you mean it opens in Xv. Xv is an image viewer.