http://www.keithjohnstone.com/videos.php
Looks like the website has a 2 minute excerpt video. I found out about it from the "I heart Keith Johnstone" facebook group which also has another preview that's 4 minute long. It's pretty fascinating.
------------------
"There is a seemingly improbable chapter on Mask work in my book Impro (Faber and Faber, and Methuen). I hope that these extracts from two classes on how to teach Masks at my July 2007 Impro Summer School will show that I was not exaggerating."
- Keith Johnstone
Keith Johnstone DVD on Trance Masks
Discussion of the art and craft of improvisation.
Moderators: arclight, happywaffle, bradisntclever