# original FPS: problem when analyzing slow motion captures

FPS = Frames per second

We can find a lot of slow motion captures on on sprinting … When you see a 100m race on TV it always have a re-play in slow motion.

Thats great! Especially for nerds like myself that like to analyze contact times etc.

But to the problem: How do you determine the original frame rate?

For convenience I always use 100 fps for my own capture so that I know one frame equals one millisecond.

When I find a clip with unknown frame rate I can often find the results of the race somewhere, so I can get the original fsp though some number crunching.

Ex: A race that took 9.85 seconds with X FPS converted to 25 fps (standard for video), in 40.55 seconds.

40.55 / 9.85 = 4,12 (times slower)

4,12 * 25 = 103 (the original frame rate was 103 fps)

So if contact time for a particular athlete in the race was 12 frames, that means his/her contact time is 12/103 seconds.

Often though, the video does not cover the entire race, and only show a section, for example 40m to finish. If I’m lucky I can see the 60m /80 line or markings for hurdles. Then I can roughly estimate the current speed to get the FPS.

Does anyone have other methods, tips and tricks? Anything that I can look for, like someone in the crowd dropping something (timing the drop, knowing the gravity), camera flashes, some biomechanic movement, etc that has a known and somewhat accurate timing.