ffdshow is a decoding and postprocessing filter that works with a variety of mpeg 4 sources, from MSmpeg4v2 & 3, to Divx & XviD, it also allows realtime adjustments of stuff like hue, saturation, noise, deblocking in realtime from its control panel.
Have captures of washed-out VHS fansubs of shows that have never been released domestically? mess with hue & saturation to get the colors to look better. A little macroblocking? mess with some of those settings, or even add a little luma noise to give it more of a soft "film" kind of look.
It's also a fairly efficient filter, and can reduce processor load while playing video, particularly when not using too much postprocessing.