How do I find movement in a video file

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http://ubuntuforums.org – I am experimenting with a DIY CCTV system using an old helmet cam. I can leave it running, and then later collect it and download the file to a computer. However hours of footage of the back yard are not exciting viewing, so I'd like something to scan through the files, and let me know where anything eventful happened. I have found lots of information about Motion, which looks great, but seems to only work with a live video stream. Does anyone know of an equivalent that works with a folder of existing video files? (Hardware)