Some years ago I built a projector, using a overhead prjector and a TFT, as most of you readers know them already. But I never did overcome the problem of keystoning. I know that you can tilt one of the lenses, but with most DIY builds this can be a quite frustrating procedure.
So after many years of looking for a solution thats easy to use, especially because I don’t want that ugly projector to keep standing in the middle of my living room and I always move it to one corner after using it. That means that i have to do the keystone calibration each and everytime I want to use it.
The solution: mplayer already has a perspective correction video filter feature included