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Recorder time drift
https://forum.ipisoft.com/viewtopic.php?f=5&t=10329		 Page 1 of 1
Author:  prisonerjohn [ Tue Oct 20, 2020 8:38 pm ]
Post subject:  Recorder time drift
Hello,

I just started working with iPi Recorder and Motion Capture, and although I've been super impressed with it so far, I'm encountering a synching issue I need help with.

My setup is using 4 Kinect Azure devices on a single PC. The PC is pretty powerful, with an i9 CPU and an RTX 2080i GPU, and I'm plugging in the Kinects in two different USB buses (2 ports per bus). The project I am working on is also recording video using a secondary camera (BlackMagic), completely independent from iPi. We need both the footage from iPi and from the video camera to be in sync for the entire duration of the piece, but this is not the case. We sync the start points of the videos with a clap but we can quickly see the iPi Recorder video runs a little faster at the beginning, then keeps going faster than the video from the camera. Both are set to run at 30fps, but it looks like iPi is dropping frames but not compensating the timecode, or something along those lines.

I have a couple of ideas I will try, but am still reaching out for help:
* I had the setting to prioritize speed (by dropping frames) turned ON. Maybe I can try with it off.
* I am also recording 720p color from the Kinects. I can probably turn those off to limit bandwidth.

Has anyone seen an issue like this? And does anyone have any suggestions on what can be done to resolve this?

Thank you,
Author:  vmaslov [ Wed Oct 21, 2020 12:58 am ]
Post subject:  Re: Recorder time drift
Hi
Quote:
I had the setting to prioritize speed (by dropping frames) turned ON. Maybe I can try with it off.

This is a playback setting only, it doesn't affect recording. And I think your issue is with recording. The actual recording frame rate is less than nominal 30 fps. So when lower FPS recording is played back at 30 fps it looks faster.
You can view live statistics including actual frame rate and the number of frame drops per camera in Statistics pane at the bottom of each camera screen during recording. Also, you can view statistics of recorded video in the player, in Video Info pane (activated by the toolbar button).

Quote:
I am also recording 720p color from the Kinects. I can probably turn those off to limit bandwidth.

Yes, reducing the bandwidth may improve the low frame rate issue (if it's your case).
Also, using a separate USB 3.0 controller per camera may help. There are PCIe cards with multiple USB 3.0 chips. You can find links to such cards on our website (look in "USB Controllers" rows). Prefer cards with NEC/Renesas chips - these chips have good compatibility with various cameras including Azure Kinects.
If you're using USB 3.0 extension cables they also may be the cause of the issue. Always use active cables (aka repeaters). You may also try to avoid cables altogether and go with multiple PCs and distributed recording.
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