• Fractional frame rates.  Don't settle for 29 or 30 when you want 29.97.
• Optimized disk access for more consistent hard disk usage.
• Create AVI2 (OpenDML) files to break the AVI 2GB barrier and multiple files to break the FAT32 4GB limit.
• Integrated volume meter and histogram for input level monitoring.
• Real-time downsizing, noise reduction, and field swapping.
• Verbose monitoring, including compression levels, CPU usage, and free disk space.
• Access hidden video formats your capture card may support but not have a setting for, such as 352x480.
• Keyboard and mouse shortcuts for faster operation.  To capture, just hit F6.
• Clean interface layout: caption, menu bar, info panel, status bar.

VirtualDub lets you clean up video on your computer.
There are lots of programs that let you "edit" video.  And yet, they're frustratingly complex for some of the simplest tasks. 
VirtualDub isn't an editor application; it's a pre- and post-processor that works as a valuable companion to one:

• Reads and writes AVI2 (OpenDML) and multi-segment AVI clips.
• Integrated MPEG-1 and Motion-JPEG decoders.
• Remove and replace audio tracks without touching the video.
• Extensive video filter set, including blur, sharpen, emboss, smooth, 3x3 convolution, flip,
  resize rotate, brightness/contrast, levels, deinterlace, and threshold.
• Bilinear and bicubic resampling -- no blocky resizes or rotates here.
• Decompress and recompress both audio and video.
• Remove segments of a video clip and save the rest, without recompressing.
• Adjust frame rate, decimate frames, and 3:2 pulldown removal.
• review the results, with live audio.

You can take a captured clip, trim the ends, clean up some of the noise, convert it to the proper frame size, and write out a better one.  Don't see a video filter you want?  Write your own, with the filter SDK. VirtualDub is fast.
The author of VirtualDub is very impatient.  That means his program is designed for speed, both in the interface and in the processing pipeline.  Converting a compressed, 320x240 MPEG-1 file to an uncompressed, 24-bit AVI requires only these two steps in VirtualDub:

• Open video file (Ctrl-O).
• Save AVI (F7).

How fast is this operation? 
On a C450, 40 frames per second (1.3x real-time speed).  With a little tweaking, the speed rises to 55 fps (1.8x), with the CPU hardly breaking a sweat at 40%. VirtualDub is cheap.
To be exact, it costs nothing.  VirtualDub is licensed under the GNU General Public License, meaning you can use it for free.  No risk involved, and the whole source code is available if you want it.

Source: Copyright © 2002, VirtualDub web site