Camera synch issue

[Jacob Harter]

Hello everyone,

i'm writing my thesis about validation of OpenCap in comparison to other established MoCap systems.
For synchronisation of the systems, i did put a visual flashlight in the viewing area of all camera systems to identify the specific synch point in both systems.
After the data collection, i discovered a delay of the flashlight between two cameras in OpenCap, so the video synchronisation does not work and the flashlight appears at two different time points in the cameras.
Is there any option, how i can fix that? Or can OpenSim fix those trials manually for me?

Thank you all
Cheers, Jacob

[Antoine Falisse]

Hi, which OpenCap videos are you looking at? The raw videos are not synchronized, but we synchronize the data as part of our algorithms and write back synchronized videos. It is possible that there is still a little delay if the algorithm did not work perfectly. Is the OpenSim data looking good? Please note that we pushed an update in the synchronization algorithm last week.

[Christina Frese]

Hello Antoine,

I have a related question. You did write that you use post-processing for your cameras. Have you checked how big the delay is in average if you have an acyclic motion, if there is any delay? And the videos to download are synchronised? Maybe a stupid question, but just to be sure. The time stemps in the videos and in the motion data are the same? So If I sync the video by a flash light, I sync automatically with the motion data? Is the information still up to date, that you guys do not plan to synchronise with other systems?

thank you for your answer, which has always been helpful,

Christina

[Antoine Falisse]

When you download data, you should have two videos per camera per trial (eg, /Videos/Cam0/InputMedia/<trial_name>; the one with _sync is after we correct for the delay. It should thus be synchronized with the corresponding ones from other cameras(eg, Cam1 and Cam2). And the synced videos correspond to the motion data (ie, OpenSim data). Please note that when you play data in the web app for the first time, the videos and skeleton are not always synchronized, it works fine from the second time. Hope it helps, we do not plan to add support for synchronization with other systems in the immediate future.

[Christina Frese]

Dear Antoine,

thank you for your answer. This helps us a lot. Thank you for replying always so quickly to my questions

best regards,
Christina