Pendulum-based method for determining the temporal accuracy of digital video-based motion capture systems

Objective: To develop a simple method to determine the temporal accuracy of motion analysis systems incorporating commercial digital video cameras. Methods: A planar column pendulum with a natural frequency of 0.872 Hz was used to analyse five systems incorporating commercially available cameras and a single codec. Finding: The frame rate for each camera was measured to be within 3% of the US National Television Systems Committee (NTSC) broadcasting digital video standard of 29.97 fps: however some cameras produced a frame duplication artefact. Least squares curve-fitting using a sinusoidal function revealed RMS differences between 3-5% for angular position and 5-15% for angular speed compared to the captured motion data. Conclusion: A simple method of evaluating temporal accuracy of a digital-based motion capturing system is demonstrated and it is shown that some digital-video cameras and computer playback software contain data compression technology that may produce substantial temporal frame inaccuracies in recovered video sequences. The results indicate that temporal accuracy should be evaluated in digital-based based human motion analysis systems prior to their use in experimentation. (C) 2008 Elsevier B.V. All rights reserved.