You're not going to have much success here... the noise the fans make is a result of their size, shape, and speed. To move the correct amount of air at a lower RPM, you'd need a physically larger fan (square mm) or a fan with blades that are deeper in pitch (thicker fan) and neither of these changes would result in a fan that would fit in the chassis. Also, even if you could make the fans quieter, your server has at drives in it which are spinning at either 10k or 15k RPM. These are also noisy.
Realize that you are using a machine optimized for high density rack deployments, which means lots of heat in a small volume, where noise is rarely a real concern. You can either live with the problem, move the server to a less noise sensitive area (I'm guessing you're streaming the video over ethernet, so it doesn't really matter WHERE the server is) or replace the server with something more appropriate for your application.
