NDI latency vs SDI

[Jason H Thompson]

Has anyone done a latency test between NDI capture and SDI capture using a Datapath Pro card?  I've been doing a lot of research on NDI and it might be a better capture option than SDI.  I'm always looking to reduce latency and improve stability, and I have a couple large live video shows coming up this year where maybe NDI would be the better solution.

 

Thoughts?

[Vollmers]

I'm planning to do exactly that test. I have high hopes for NDI vs. SDI, and my recent test with NDI were very promising. So let's share our results, to compare.

[Miro]

I did quite a lot of testing before the summer and it's the same delay using DataPath SC SDI card as using the DataPath LC SDI card. I had the following setup:

 

 

Where I connected a SDI source (with frame numbers) to a splitter. One of the outputs of the splitter was connected to a computer equipped with a capture card. The signal was captured and transmitted using NDI to a WATCHMAX server that displayed the image on a low latency monitor. The other output from the splitter was connected directly to another identical monitor. The both screens were filmed with a 240 Hz camera so I could measure the frame offset.

 

For 720p60 and 720p59.94 I got 4 frames offset which is roughly 67 milliseconds. The type of content didn't really matter.

 

At this time I used NDI v2 and the current version 3 is probably slightly more efficient. I will try to find some time and test this with the updated SDK version and also 1080p60 and 2160p60 resolutions. We also got the BirdDog NDI converter today so we will test that one as well.

 

Just running the capture card locally in the WATCHMAX results in 2-2.5 frames latency between capture and display. So if 4 frames are acceptable then NDI is much more cost efficient since most of your servers doesn't need capture cards. Great when using WATCHPAX units.

 

//Miro

[mitreklov]

Hi Miro,

 

Out of interest did you use the same capture card type (Datapath?) for the SDI - NDI conversion as was fitted to the WATCHMAX?

 

Please update this thread once you have had a chance to test the BirdDog unit, very interested to find out how these work out.

 

Thanks

 

Tim 

[Miro]

For the SDI to NDI conversion took place in a different computer. This computer transmitted over standard gigabit network to the WATCHMAX that received and displayed the captured stream.

 

I created a custom software (based on libAV/FFmpeg) for the capture to NDI where I could optimize the flow as much as possible. Datapath can convert RGB to UYVY directly in the capture card and since NDI uses the UYVY-format no conversion needed to takes place which reduces latency slightly. Also a less powerful computer can do the job so I actually used an Intel NUC or my laptop as NDI server (with a thunderbolt3 PCIe expansion box for the capture card).

 

I just noticed that FFmpeg 3.4 added native support for NDI so I will test that one too.. 

 

We briefly tested the BirdDog and first noticed that it's only using TCP (NDI v2 or older) so we could only stream 1080p60 to 5-6 computers before frames started to drop. Probably hitting the bandwidth limit of the 1 gigabit network. After 8 streams it gave up. So don't expect it work with larger clusters and it's probably intended as a peer-to-peer device. Didn't measure any latency this time.

[pdm]

Have you tested Full NDI cameras to eliminate the sdi to ndi conversion?  Have you tested NDI HX cameras in that same sense? I am looking for this information and it is very hard to find. This thread from 5 years ago is the closest to answer I have found so far on google.  I am trying to understand what the lowest latency NDI can achieve.  If there are other active threads that discuss this better, please let me know.