I say: Converts between mpeg and avi video formats letting you recompress, clip, and filter the video to your liking... and a whole lot more.
They say: " VirtualDub is a video capture/processing utility for 32-bit Windows platforms (95/98/ME/NT4/2000/XP), licensed under the GNU General Public License (GPL). It lacks the editing power of a general-purpose editor such as Adobe Premiere, but is streamlined for fast linear operations over video. It has batch-processing capabilities for processing large numbers of files and can be extended with third-party video filters. VirtualDub is mainly geared toward processing AVI files, although it can read (not write) MPEG-1 and also handle sets of BMP images.
I basically started VirtualDub in college to do some quick capture-and-encoding that I wanted done; from there it's basically grown into a more general utility that can trim and clean up video before exporting to tape or processing with another program. I released it on the web and others found it useful, so I've been tinkering around with its code ever since. If you have the time, please download and enjoy."