This is a tool to extract motion vector from a mpeg video. I modified this from original code somewhere back to 2007 when I'm a grad student, but it's never maintained after that. From time to time, I receive email about how to modify the code or things like that. Since I no longer work on that for years, I think it might be better to publish on github to encourage forking, hoping others to benefit from it.
You'll need libavcodec and libavformat. Back to that time, it was shipped with ffmpeg on Debian.
Original post in Traditional Chinese: http://victor.csie.org/2007/06/motion-vector-extraction.html