If you care about the size of the Fraps capture you're doing it wrong. Your capture should be in as high quality as possible, unless you don't have the hard drive space. But 20 minutes of Fraps footage even at highest quality isn't much of a hardship. The resulting Fraps file(s) are known as an "intermediate" file, which you then render in something like Sony Vegas and/or Handbrake to a format suitable for distribution. If you worry about the size of your capture files, the quality of your final video will be compromised. Once you've made your final version, you can delete your capture files, and then how big they were doesn't really matter.
