How to obtain framerate while running preview

I would like to obtain the framerate while running preview for a videoinput object. I would like to display the framerate dynamically while preview is running. This is apparently more difficult than collecting a sequence with start and stop commands and obtaining timing information afterwards from the videoinput object using 'getdata'. The framerate is already displayed dynamically inside the imaqtool,- I just need the Matlab code to do it.