With UT, you can open the System Console and type in:
timedemo 1
hit Enter
open cityintro
and hit Enter
Then hit the tidle key ~ and the Esc key when you hear the music change.
It will loop until you stop it.
Or you could start a practice session with what ever number of bots you normally play with.
Set the Frag limit to 999, let yourself get killed and it should run for awhile.
