VDO Latency

[Cacsjep]

Hey Axis Team,

We are currently developing a viewing client for industrial applications and have reached a point where VDO latency is a major value in the chain. After several tests we came to the conclusion that it seems that VDO itself has a high latency when we assume a near real-time display.

Our rendering plus decompression for JPEG takes less than 25ms. With the VDO latency, this results in an end to end latency of about 50ms. We have tested and validated this in several different tests.

However, this has been an experiment to see how far you can reduce the end to end latency. Our final solution is a browser based one. To have a better cross platform solution. Here we have an end to end latency of about 65ms.

If we use VDO_TIMESTAMP_MONO_CLIENT_CAPTURE_DIFF and compare the timestamp, the image already has a latency around 22ms. So before we do anything with the image we already have this latency. That would be around 33% of the total end to end latency with our browser solution.

We also see that there is a tool on the camera (vdo-client) that shows similar values for latency. I also checked this latency by placing the camera in front of a 240Hz monitor with a millisecond timer and then comparing the image timestamp with the timestamp on the monitor, in the captured frame. (Saved directly on camera with .jpeg)

Setting buffer.count on the VDO Map does not make any diffrence,

Testing vdo with the existing axis tool. (AXIS Q1615 Mk III 100FPS, ARTPEC-7)
/usr/bin/vdo-client -n 20 -t yuv -o /dev/null -s -c <compression> | grep vdo.latency.

Testing vdo with the existing axis tool. (AXIS Q3536 Mk 60FPS, ARTPEC-8)

I did our tests with Low Latency mode activated and all image optimizations turned off. Also no rotation, overlay, Privacy set. etc..

The only really thing to reduce VDO latency is when I decrease the resolution, but thats not an option for us.
Also tests show that with higher resolutions, VDO latency is increasing, but not for YUV, so it looks to me that maybe compression is here the factor of latency.

Of course I can imagine that there are a lot of things going on in the background, but maybe you have an idea or info for me how I can reduce VDO latency without changing the resolution even 10ms savings would be great, or maybe tune some internal compression params for jpeg. If this is not possible, then it is just so, then this is so to speak state of art.

Thanks
Br Christoph

[Cacsjep]

Support has answering me that question =)