Split or Mark video file using Motion Detection

I've searched but cannot find a free or trial utility for motion detection on a file.

I have a long .wmv file recorded by a web cam (i.e. not great quality) and I need to cut out large sections of just background without motion.
I may need some settings to mask out a fish tank or set the threshold below that small motion. Even a tool that produced a log of the times where a relative amount of motion occured would help do the job.

Anybody know of such a utility for this?

I've also looked for "virtual camera", to make my file look like a camera device so that I could use motion detecting utilities set up for cameras. Is there such a driver that works with a simple webcam based motion detecting video recording utility?

Thanks for any suggestions.

Michael