It is already compressed. You can use a video editing program to reduce the quality of the video to make is smaller. E.g. you can cut out unneeded parts, make the video image smaller, reduce the framerate, use more aggressove compression..
The reason I wanted to know was to be able to make
a video file small enuf to email - then I discovered
places like www2.sendthisfile.com where you can send
virtually unlimited file sizes for free.