Hello,
I’m excited to start testing the Zed GMSL2 camera ecosystem for some of our use cases, starting with the Zed X Mini, and I seem to be running into much longer than expected latency. This makes me wonder if I’m doing something wrong and whether someone could give pointers to whether my assumptions are correct and what may be wrong about my set-up or assumptions.
My expectations are based on the following forum posts:
- https://community.stereolabs.com/t/gmsl-zed-x-vs-regular-zed-and-usb-cable-latency/2681: according to this post the expected latency with GMSL2 is 1-2 frames instead of a USB3 camera’s 3-4 frames
- https://community.stereolabs.com/t/latency-measurement-of-the-zed-mini-camera/3712/2: this post shows the expected 3 frame latency for a ZED Mini USB camera of ~50ms.
During my testing so far I am seeing worse latency with the GMSL2 camera than with the reported ZED Mini USB camera in the forum post above.
Latency I’m seeing:
- Zed X Mini SVGA@120fps, 1ms exposure: ~85ms (= ~10.2 frames)
- Zed X Mini SVGA@60fps, 1ms exposure: ~134ms (= ~8 frames)
- Zed X Mini SVGA@15fps, 1ms exposure: ~185ms (= ~2.7 frames)
- Zed 2i VGA@100fps, short exposure: ~76ms (= ~7.6 frames)
- Zed 2i VGA@15fps, short exposure: ~86ms (= ~1.3 frames)
Zed X Mini’s latency is significantly above the 1-2 frame latency and even 3-4 frame latency for higher framerates. Zed 2i’s latency is also significantly lower in these tests than Zed X Mini’s, especially for low framerate configurations where the USB3 camera even achieves a ~1.3 frame latency which is unexpected based on the information linked in the above section.
Latency measurement setup(s):
- Method A: same as described in the forum post above, running the stopwatch tool on the monitor and viewing it with the camera, taking a screenshot several times and calculating the delta
- Method B: python script connected to the camera generates a qr code on the monitor encoding the current timestamp and waits for a camera image. The delta between the time an image arrived and the encoded timestamp in the qrcode in that image yields the latency. Latency is averaged across 100 frames with detected qr code.
- Both methods use a 60fps monitor attached to the Jetson X. It’s not a very fast monitor however the latency I’m seeing are well outside the expected range even with the 1/60s measurement uncertainty.
- The latencies reported in the section above stem from Method B and were verified against Method A.
System set-up:
- Jetson Orin 64GB Developer Kit running in MAXN power mode
- ZED Link Quad Capture Card, powered via 12V 5A power supply
- Single Zed X Mini camera plugged in via 5m fakra extension cable + 1-to-4 fakra cable
- No other system load on the jetson
Thanks,
Thomas