It's also on the bonus disc of the Greatest Video Hits I DVD.
This site (http://www.ultimatequeen.co.uk/Videos/queenpromo.htm) has this to say about it:
We Will Rock You
Fast (Live) Version
Directed by Rock Flicks
Filmed at 'The Summit', Houston, Texas, December 1977
Filmed during an actual concert, with some audience noise.
Available on 'Greatest Flix' and 'Greatest Video Hits I'