Topic: Time units - why does Kinovea calculate 50ms steps?

I have a video with 1 frame = 1 ms. When changing the settings for time units from framenumber to milliseconds, Kinovea (v. 0.9.4) returns 50ms steps, so frame 1 = 0, frame 2 = 50ms, frame 3 = 100 ms, and so on, instead of frame 1 = 0ms, frame 2 = 1ms, frame 3 = 2ms. As calculations such as angular velocity depend on the correct time unit, I was wondering if anyone could help me with this problem. Many thanks!

Re: Time units - why does Kinovea calculate 50ms steps?

Most probably the device that recorded the 1000 fps video marked the file as 20 fps, this is common. You should go to menu Video > Configure video timing, and in the "High speed camera" section, set the frame rate to 1000.

Re: Time units - why does Kinovea calculate 50ms steps?

Dear Joan,
thanks for this helpful reply - it worked.
However, when I cross-checked the calculations performed by Kinovea on angular velocity with my calculations, I noticed that the results are not congruent (but within the same range). Of course, this can be a brain issue on my behalf but I can't find the error and was wondering how Kinovea calculates angular velocity - also ??/?t? Or may I send you a quick outtake of my results (Excel?)
Many thanks!

4 (edited by joan 2021-Sep-20 12:50:09)

Re: Time units - why does Kinovea calculate 50ms steps?

Most probably the difference is coming from the extra smoothing pass which is done for high speed footage for velocity and acceleration. This was added because the small time intervals amplifies the digitization noise on the derivatives.

For the next version I have added an option to disable this in the preferences so you can get the raw data. Disabling the main smoothing will also now impact how curves are drawn in the graphs and tracks.

edit: Actually this extra smoothing wasn't implemented for angular kinematics so I'm not sure where the difference could be coming from.