making on indeterminate progress bar?

making on indeterminate progress bar?

There is a nice animated progress bar here in the demos:
http://jqueryui.com/progressbar/#animated

How do I get such a nice animated gif from themeroller?  Where did that graphic come from?

I want it so that I can make an indeterminate progressbar.  The links about an indeterminate progressbar are all pretty stale.  However, it is mentioned in the API

"if the actual status cannot be calculated, an indeterminate progress bar or spinner animation is a better way to provide user feedback."

What is the best practice in early 2013 for making an indeterminate progress bar?