A very outdated description:
ffdshow is a
DirectShow decoding filter for decompressing DIVX movies. It uses libavcodec from ffmpeg project or for video decompression (it can use xvid.dll installed with xvid codec too), 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.
Video decoder features