Webcasting with Ustream

A question for those who have been involved with webcasting competitions with Ustream: How have you gone about inputing the video/audio feed from the event? I’m only seeing an option for broadcasting a webcam with Ustream. Is an external video capture device required, is there a USB input method, or have you used a computer that was already part of the event A/V system?

Here is a thread I had bookmarked from a while back

I imagine if you have any other video input device ustream would allow you to webcast that, it is just a matter of having one.