I worked on this project where we needed to analyze the motion of objects from the camera in real time. We were trying to find an algorithm that was fast enough

I worked on this project where we needed to analyze the motion of objects from the camera in real time. We were trying to find an algorithm that was fast enough to run on the hardware, but to no avail. One day, it dawned on me that since our hardware encodes the video in h264, we should be able to get some of that info from the video itself. So we tried extracting the motion vectors from the video and sure enough, it was good enough for our use and we got it basically for free.