Well, it's not as easy as you might hope. Here's a thread at the FDS users forum that lists 3 different ways to go:
http://groups.google.com/group/fds-smv/browse_thread/thread/a1f53bee9609d9b7
Your options are basically:
- Save out a bunch of still images, then stitch them together into a movie using another tool.
- Use a screen recorder and manually control Smokeview while you record the video.
I've seen good results from both techniques.
- Charlie