1 Topic by Robbins

  • Robbins
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Hi,


I am trying to use a PS eye camera to capture video files directly in to Kinovea. I have installed the driver which allows the PS eye camera to be located in the menu and offers a wide range of options for frames per second (up to 187 FPS depending on the resolution).

However, if I go above 45 FPS in the higher resolution or 100 FPS in the lower resolution the file does not save correctly. There are two errors that occur. Firstly the file plays back at a faster rate, as if watching at increased speeds, secondly the time (as monitored with the stopwatch tool) is not correct. Usually the time is too short compared to the genuine duration of the recording.

I note that as I repeated the measurements, testing each FPS option in descending order, the errors reduced until I reached 45 FPS in the higher resolution or 100 FPS in the lower resolution. At lower FPS the recordings seem to be accurate. Based on the observation that the lower FPS setting function correctly I assume that this is not a driver problem? Would I be correct in assuming that the laptop I am using does not have a powerful enough processor and/or graphics card? I am using a Toshiba ultrabook with a core I3 processor. I was wondering if would need something like a core I5 or core I7 to get the faster frame rates working?

I have checked all the previous thread and have not seen anything else posted indicated this has been noted before so any feedback would be great!

Thanks

2 Reply by joan

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Hi,
The "playback is too fast" problem arise when we select a framerate but we do not receive the frames at the advertised rate.

Due to something else, PC being busy, camera giving wrong info, etc. we receive images at a lower rate. We still save the advertised framerate in the file metadata for a lack of a better value. So when played back, it plays at the advertised framerate even though frames were captured at slower rate. Hence the speeding up of the action.

If you use 0.8.21, the actual framerate at which frames are received is displayed in the top bar above the viewport. You will probably see a lot of variability when choosing higher framerates, and more stability for lower framerates.

At the moment I do not know how to mitigate this problem. Saving the actual framerate seen when the record button is hit is not really an option since it's very variable. Maybe keeping the average of the framerate of the sequence and using this, but the issue is that the metadata is written before the capture starts…

3 Reply by Robbins

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Thank you for the reply, the insight is very useful. It is certainly above my level of understanding, though for the sake of trying to be helpful I will offer one idea - is it possible to have a 'calibration period' where the software records the framerate from the top bar? An average could then be obtained to set the metadata?

No idea if this would work but might be worth a try?

Thanks again

4 Reply by joan

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Yes, I had thought of this but the mere fact of saving to file is adding burden to the CPU from the extra copy of images and access to disk, so an average computed before recording starts would still overestimate the true framerate of the capture…

A more ambitious solution would be to record in a dedicated format with timestamps associated with each image and honoring the timestamps at playback time. It would break compatibility with other softwares though.