ffdshow is a DirectShow decoding filter for decompressing (watching) DIVX movies
From the Official Site :
ffdshow is a DirectShow decoding filter for decompressing DIVX movies. It uses libavcodec from ffmpeg project for video decompression, postprocessing code from mplayer to enhance visual quality of low bitrate movies, and is based on original DirectShow filter from XviD, which is GPL'ed educational implementation of MPEG4 encoder.
Features :
fast video decompression using optimized MMX, SSE and 3DNow! code
support for different codecs: XviD and all DIVX versions
image postprocessing for higher playback quality
automatic quality control: automatically reduces postprocessing level when CPU load is high
hue, saturation and luminance correction
experimental sharpening filter
completely free software: ffdshow is distributed under GPL
noising (of course if you want it)
Playing back .MP4 H.264 encoded movies:
Use VideoLAN which has a built in .MP4 reader and H.264 decoder