http://www.kinovea.org/
Kinovea is an open source (GPL-licensed) video tool to help analyze motion. It lets you load up a video file and adjust playback speed for slow/fast motion, frame-by-frame advance, do overlays of timers, draw lines on the image, angle indicators, perspective grids, do split-screen comparisons, etc.
Enjoy.
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http://www.polycount.com/forum/showthread.php?t=55102