I've spent a lot of my evening browsing the Texas Archive of the Moving Image website. A lot of the Austin-related footage was donated by a cameraman from the television station KTBC, so it's mostly from the 60s and covers the spectrum from shots of the Butter Krust Bakery bread truck fleet to film of a memorial service for JFK at the State Capitol. A lot of it is silent and unedited, but it's still fun to see the landscape and how it's changed in the last 40 to 50 years.
They also have a nice round-up of the history of Austin up to 1962 and random families' home movies and I'm sure a lot of other stuff I haven't found yet. You should go poke around if you like that sort of thing.