so what is post-processing

[thmanx]

I see that i can do post-processing in some movies, what does it do?

[yoann]

On some particular streams (MPEG 4, DIVX, ...), some additional image filtering can be applied to the video before display, improving its quality in some cases : for instance it can reduce the blocking artefacts on low-quality videos;
Different levels of post processing can be chosen. A higher level means more filtering.