[ excerpt from developer's www site with modifications ]

The idea was to use the high performance Metakine M2Requantiser to
create a transcoder for Linux for shrinking the content of a DVD9.
This would enable backups on cheap single layer DVDRs (double layer
burners weren't even available that time).

Vamps builds a wrapper around the requantizer to extract the
elementary MPEG2 video stream from the DVD's program stream, feed
it through the requantizer and finally re-pack it into the program
stream again. Besides this, Vamps allows the selection of both audio
and subtitle streams that should be copied into the output stream.
This gives another small gain of disk space, since unwanted streams
may be discarded.

Summed up, Vamps is only a very basic, but nevertheless essential
tool to transcode DVD videos to a smaller size. Vamps does not need
to write temporary data files, which is a major pro. Vamps is very
fast. The downside is, that Vamps is not capable of making DVD
backups on its own.