I believe 9600 is the capacity and the event has been sold out since shortly after it was announced.
Crowd at Red Rocks has many more young people than typical Romney crowds. #2012
— Kasie Hunt (@kasie) October 24, 2012
For those like the panoramic shots: http://360.io/nRThPH
Thanks to John in the comments section, here is the actual live video feed: http://www.9news.com/news/article/295708/339/LIVE-VIDEO-Romney-Ryan-at-Red-Rocks-