This is not a "performance" or a general introduction. Instead it is a somewhat congested, and probably confusing, introduction to some of the more technical aspects of Extempore. In particular concurrency, the compiler, audio signal processing, and runtime binding to dynamic libraries.
It's almost certainly premature to be making screencasts with Extempore, however, I've thrown this together because, as they say, a screencast is worth a thousand words.
The audio is slightly out of sink but this shouldn't cause to much trouble for this introductory video.
In this screencast Extempore is running in Emacs under Ubuntu Linux.