LED Sync issue over 2 vertical outputs

[plbrunet]

Hi everyone,

We have a permanent installation with an LED screen (1984x1216) driven by 2 outputs setup vertically. 1 on top of the other. (each at 2048x1080) Coming from of 1 Player Pro, 1 graphic card (Nvidia GTX970) and there are synchronization issues between the 2 outputs. When there are some horizontal movements happening at the junction of the 2 outputs is when we see that the 2 outputs are not fully in sync.

We have a second installation with the same system, same LEDs, LED processors, etc but with 6 outputs side by side horizontally and it works fine so I think the issue here is related to the fact that this setup is vertical. I've joined an image showing the screen/outputs layout.

Have you guys ran into this problem before? Do you know how we could go about solving this?

Thank you.

[Dennis Kuypers]

Hi,

I never tried, but in theory: Flip the upper screen vertically (physically) if it is a 1x2 array.

Problem arises from the fact that screens refresh top-bottom. Most of the time the "next" frame on the lower screen's upper half will meet the upper screen's lower half which is still showing the "previous" frame.

Other solutions:
- use a controller that treads the two screens as one large screen and makes the refresh one after another
- increase frame rate to lessen the effect
- don't do horizontal movements
- do very slow horizontal movements
- offset the lower screen with the Video Delay FX
- play the lower half video with 1 frame delay (screen refresh rate!, not video frame)
- rearrange the screens to side by side

Regards
Dennis

[plbrunet]

Hi Dennis,

You are probably right that the display would need to be physically turned upside down. Unfortunately sometimes, that's not possible. I tried doing a rotation for one of the outputs in the nvidia settings and it didn't fix the problem.
But I had a conversation with Markus about this when I was at your office this summer. He was telling me about this issue with the example of a 9x9 video wall but I wonder what his actual solution was. What is to physically flip the TVs or is there another software/settings solution?

We also found that using an Nvidia Quadro in MOASIC mode fixed the issue because then all combined outputs have 1 common refresh rate. But of course a Quadro is more than double the price of a GTX970.
That being said, The Nvidia NVS series also have the MOSAIC feature. Have you guys or anyone else worked with these video cards in Pandoras Box? Some models are in the same price point. It seems like the NVS 510 could do the trick.
http://www.nvidia.ca/object/nvs-product-overview.html

What do you think?
Thanks.

[Daniel Kaminski]

Hi,

the NVS Cards will propably not do the trick.
The problem is they are made for Desktop Application Use like Word and not for video realtime rendering.
We checked those cards once and found that everything under the K2000 does not have enough GPU and rendering power.

The card might work for you if you are looking at displaying only images and no videos.

Daniel

[Dennis Kuypers]

Hello,

rotating the output in nvidia doesn't make any difference. You need to rotate the screen. The Quadro and Sync can not solve it either. Still the same issue.

I updated by previous post with solutions and worarounds.

Dennis

[justyn roy]

I've had this issue before.

I was able to fix it by putting the displays side by side in Windows, and then using the Camera X&Y offset to place the second output below the first one.


Justyn

[plbrunet]

Hi guys,

@Dennis
Other solutions:
- use a controller that treads the two screens as one large screen and makes the refresh one after another
(I believe that's what the Nvidia MOSAIC does. It seems to work)
- offset the lower screen with the Video Delay FX
(It seems we would need servers to use this effect. We have Player Pros. The Refresh Delay effect anyway.)
- play the lower half video with 1 frame delay (screen refresh rate!, not video frame)
(How would we go about doing that? I looked in the Nvidia settings and did not find anything.)

@Daniel
That's interesting about the NVS. The Nvidia websites boasts of being able to do "spectacular wall display for digital signage." And says that it is: "The new standard for MULTI-display commercial graphics." But looking at the spec we see that it is quite a bit less powerful than a Quadro M4000 which is what we are using on our other computers. We will likely end up buy more of those for this installation. Thanks for the tip.

@Justyn
At first our 2 displays were side by side in windows but are in fact physically one on top of the other. I tried a few combinations of positioning in windows but with no positive effect. I'm not sure how it would have helped your case... But if it did, all the better, it didn't change anything for us though.

At the moment it seems like the Quadro in MOSAIC mode fixes our issue.
The Nvidia website says this about the Mosaic:
"Seamless Image*
See a flawless image without any tearing artifacts from a fully synchronized display environment."

It appears to be true. In our tests so far, it did fix the issue. Hopefully it be true for all case scenarios.

[Dennis Kuypers]

Hello,

- use a controller that treads the two screens as one large screen and makes the refresh one after another
(I believe that's what the Nvidia MOSAIC does. It seems to work)

Mosaic will make all screens refresh at the same time, but that's not what you want (to solve the issue). You would want to refresh screen one first and then screen two.

- offset the lower screen with the Video Delay FX
(It seems we would need servers to use this effect. We have Player Pros. The Refresh Delay effect anyway.)

Yes it is a Server-Only effect. Listing it for completeness.

- play the lower half video with 1 frame delay (screen refresh rate!, not video frame)
(How would we go about doing that? I looked in the Nvidia settings and did not find anything.)

Assuming that you have two clips, one for the top half and one for the bottom half then you could start the top clip at 00:00:00:00 and the second at 00:00:00:01. This would lead to one frame offset. You timeline should be set to the refresh rate of the screen though.

At the moment it seems like the Quadro in MOSAIC mode fixes our issue.

Mosaic doesn't fix the issue, it reduces the visibility though. If it reduces the issue far enough for you to be okay with then we have solved it.

Analogy: Lets say you watch a 30fps clip and complain that it looks jumpy / the movements are not fluid. I then show you the same clip in 60fps and you say that the problem is solved. In fact it is not solved, it just got harder to notice. For some people you may have to step it up to 120hz/144hz or beyond.

The Nvidia website says this about the Mosaic:
"Seamless Image*
See a flawless image without any tearing artifacts from a fully synchronized display environment."
It appears to be true. In our tests so far, it did fix the issue. Hopefully it be true for all case scenarios.

Well they are not wrong. They are free of tearing...it's the displays that introduce the problem.

Regards
Dennis

[satanete666]

Someone try to use nvidia sourrond in 1x2 theorically 2 outputs are in genlock

[Dennis Kuypers]

Hello,

Please have a look at the following illustration. Genlock/Sync does not solve the issue that i'm trying to describe.

genlocked-screen-tearing.png

Regards
Dennis

[plbrunet]

Hi Dennis,

Thank you for this graphical explanation. I understand that Genlock does not solve this issue. That is clear. What is less clear to me is the Moasic setup.

You believe that Moasic will not solve the issue but from the eyes of our staff on site, it's clear that Mosaic solves our issue. So I tried to get a detailed confirmation from Nvidia as to what is actually going with refresh rates while using Mosaic. Here are 2 of their responses below.

When creating a Mosaic with multiple displays within 1 GPU, all the monitors use a common refresh rate.

and

The refresh rates occurs on the complete image as a whole.

You may refer to the link provided below for reference and more information in this regard :-
https://nvidia.custhelp.com/app/answers ... trol-panel

It's not 100% clear but it seems they are are saying that there is 1 single continuous (sequencial) refresh rate for all involved outputs. It would make sense to me especially because this solution works perfectly for us. We implemented it on both LED screen installations. 1 vertical setup and 1 horizontal setup and in both cases this fixed issues that appear and look like tearing.

Side note: What's interesting on the other hand is that we use the Quadro M4000 with the sync cards for the horizontal 6 outputs installation to sync all 6 outputs over 2 players but some sync issues were showing up even though is sync setup was all good. So something was not working with the sync setup... Now we've setup the 2 Moasics and synced them with the Nvidia sync cards and no more issues.

Bottom line, this setup works great and everyone is happy.

[Dennis Kuypers]

Hello,

good to hear that you got your issues resolved! Setting up sync is tricky and you have to double check, well actually, triple check if the sync is now enabled and working.

For completeness:
I used a high speed camera to capture a 1x2 Mosaic setup on a M4000 and it does not refresh the screen as one large unit. It just does the regular pixel-clock-sync (as shown in the illustration above)

Regards
Dennis

[plbrunet]

For completeness:
I used a high speed camera to capture a 1x2 Mosaic setup on a M4000 and it does not refresh the screen as one large unit. It just does the regular pixel-clock-sync (as shown in the illustration above)

Wow, well that's very interesting! Then I don't know why it fixes our visual issue but it somehow works... Not gonna complain about that.

Thanks for the detailed analysis.

[shopp1984]

hi，i have same issue in led wall，my server output 2 4k to led processor and side by side，but it is not sync，i tried to use MOSAIC with 2 4k，but output become black，do we have other way to settle this issue？

[Benni_M]

If you have 1 device that have a edid with 50 and one with an different refresh rate connected than the fullscreen goes to black. You need a edid manager or set the edid correctly that both outs are the same.

I had this a few times...
Maybe this solves the problem.
Best,
Benni