insert video filter

i would like to find out if this is possible and how to do it if so. i want to create (in C) a video filter that goes between Firefox or maybe even Mplayer and the library calls or kernel interface to fix some poor quality (dark, bad color temp., bad white balance) while i am watching the video. or maybe it is better to write or mod a player to do this. several websites have these issues (so, solution cannot be website specific). any ideas?