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Old 07-28-2012, 06:40 PM   #17
Chas Tennis
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Join Date: Feb 2011
Location: Baltimore, MD
Posts: 4,119
Default Slo Motion Viewing, Stop-Action Single-Frame and Videos for Display

Originally Posted by jaykay View Post
Thanks for taking all the effort, Chas. How does one do slo-mo? Is this all done post-processing?
(Sorry for all the q's - total newbie here...)
I am interested in tennis stroke analysis and shoot high speed videos at 240 fps always using faster shutter speeds to reduce motion blur. I use mainly stop-action single-frame analysis of the videos to identify what is missing, done wrong, poorly timed, etc., in my strokes. I easily find many issues to work on. Since I take videos at 240 fps and they are played back at 30 fps, time is already stretched by 8 times just from the 240 fps/30 fps ratio. In addition, the Casio FH100 viewing screen is large, about 3" across, and I do a lot of viewing and editing on the camera itself. The FH100 will also playback the 240 fps forward or backward at variable slow speeds. My need for showing videos to others is very low so I have not done much video editing. If I had 60 fps to view in slo motion I would view it either on 1) Quicktime - QT can play back at 1/2 speed or 2) Kinovea Version 8.15, variable playback speed from 3-198% of original playback speed. Both QT and Kinovea are free. But again, so far, I do almost all single frame analysis with just a little slo motion playback.

Editing to Display Videos at 30 fps. Take a video at 30 or 60 fps and stretch it to make a new video that displays for a much longer time. To display a video slowly there are video editing programs that will basically repeat a frame a few times or more for display at 30 fps- so that the faster things can be observed when displayed at 30 fps. There are also more sophisticated video editors that will compute intermediate false frames between the real frames and make a new video that plays slower. I consider those techniques to be for display purposes and not for analysis.

Example, a fast event videoed at 60 fps with fast shutter. Musket firing that lasts about 0.12 seconds stretched by video editing software to display for 3.5 seconds for understandable viewing at 30 fps playback.

Last edited by Chas Tennis; 07-29-2012 at 10:12 PM. Reason: added link to example, added Kinovea playback speed
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