I worked on a project where I extracted the motion vectors from the h264 encoded stream from the camera, to detect motion. It's like a basic motion detector for free.
It's been a long time. But I remember I started with this page [0]. There are also many resources on github, like [1] or [2], but I haven't tried them.
There is a github project called pikrellcam that utilizes motion vectors generated from the raspberry pi's gpu to detect motion. It's a relatively simple piece of code and it works very well
