Sync video card outputs setup with Datapath 4x

At our festival right now we have a 4 XGA projectors setup with a Datapath 4x, plus 2 FullHD monitors, running nicely on a GTX1080.
We want to extend our screen and use 5 projectors. The solution would be to buy a Datapath FX4, then link the 4X thus getting up to 8 synchronized projectors.
Due to budget issues we can’t afford the 1700 euros of the FX4 so either we ditch the extension or we … I find an alternative solution.
I can try to use the 4X and connect the 5th projector to another output of the graphic card, it is obviously going to be out of sync (both because of different latencies in 2 different outputs, and of the latency introduced by the 4x). is there a way to add an arbitrary latency to an output ? I may try to offset that manually.
Also is there any tool I can use to assess synchronization of displays instead of the naked eye technique? Maybe a camera and some line patterns on the projectors?

Hi @io
I have no advice about how to add latency, but I can tell you how I use to check latency between input and output, this method could be used to try to sync your outputs.
I display a text showing a frame counter ( frame count output of the mainloop ).
I take pictures with my photo camera of all displays, at a short exposure time, and I compare the frame number displayed.
This allows you to know the amount of frames you’re " out of sync ".
Of course this will allow you to come close to a sync, but not a real one. It’s not a Genlock or a Framelock…

if it is so bad you can delay the fastest output by adding a pass and queue it a couple of frames

would adding another gtx 1080 give you the opportunity of being able to run maximum 8 displays??

I never did that but if it works that would be more of a budget version then the fx4.

In my experience the less outputs you use the better it is, as long as you don’t go for Firepro/Quadro cards. Not to speak about WIndows configuration, SLI setup, different kind of connection, etc.

I agree with @io , I also really prefer to use one 4K output and a Datapath than using 4 x HD outputs on a GTX GPU.

may I ask why?

I have no very concrete pro or cons, that’s just a general felling that I have in the workflow.
Dealing with multiple outputs has been painful in some situations ( EDID issues, dis-reconnecting monitors, etc… ).
I might add that my field is performing arts, so seting up the complete install a lot of times. My experience is maybe not valid for long term installs for example.
I find the workflow with a datapath “grid” much softer. You’re never getting any issue with screen arrangement, you can easily simulate the complete setup with an UHD screen.
Again it’s not here for me a question of pure performance ( fps ), more a general feeling that I have, saying " Hey, I’m less loosing time dealing with my outputs !"

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