Post-production workflow for a 2x3 display array?

[Scott Wilkinson]

(I did a quick search for this and didn't find anything immediately relevant...and wasn't sure where to post it hence it's here!)

We're going to be developing a video for use on a 2x3 array of 50" flat-panel displays (all joined together as one large display). I know this is done all the time...but I've never done it! :-) So I'm just wondering about the process and workflow.

Mainly, I'm wondering if the most common method is to create a single video sized to the dimensions of the whole array (e.g. 5760x2160) and just split the image in post however we want (based on the 2x3 grid)? Or does something like this require multiple, separate video files that are sent to different displays? (I'm guessing the first approach is what's done...but again, I've never done this!)

Any basic info is appreciated!

Thanks,
Scott

PS - The project is still in early pre-production now and I don't have the specs yet for the hardware being used to drive the array...

[Eric Olson]

Unless you have 4K source, I would suggest editing at 1/4 frame or 2880x1080 resolution.

[Scott Wilkinson]

Thanks for the reply Eric. It's been a while since my previous post...but we've got to start production on this multi-display array...and I'm still struggling to get info on production specs. The hardware vendor is supposed to be giving me a call today or tomorrow...but I've continued to be somewhat surprised that this seems like such "voodoo," since multi-display video arrays are pretty common these days.

I would think the hardware would be standardized, and the switching/distribution technology would pretty much be the same for any array...and that there would be standard formulas/methods for how the video signal is split (or combined) across the multiple monitors?

Scott

[Chris Soucy]

Hi, Scott.................

Why not drop these folks a line, they seem to have this pretty well off pat.........

Matrox Graphics - Products - Display Wall Products - PPX Series - PPX-OUT8/OUT-4

If they can't answer your questions, don't think anyone can.


CS

[Sareesh Sudhakaran]

Originally Posted by Scott Wilkinson

We're going to be developing a video for use on a 2x3 array of 50" flat-panel displays (all joined together as one large display).

Mainly, I'm wondering if the most common method is to create a single video sized to the dimensions of the whole array (e.g. 5760x2160) and just split the image in post however we want (based on the 2x3 grid)? Or does something like this require multiple, separate video files that are sent to different displays? (I'm guessing the first approach is what's done...but again, I've never done this!)

Some questions to ponder:

1. What is the average viewing distance?
2. What kind of footage is being played - text, 'detail-oriented', or 'general'?
3. What will the ambient lighting levels be like?
4. What is the ppi of each display unit/panel?

Just because the combined resolution of the display is 5760x2160 doesn't mean you actually need that.

A simple rule of thumb (not etched in stone) is that the minimum viewing distance is roughly 3x the height of the display. In your case, since you're using 50" panels, the total height is approximately 50" and the minimum viewing distance is approx 150" (or 12.5 feet). If your average viewing distance is closer than this, your display is too large.

A good consumer panel has a ppi (pixels per inch) of approximately 100 (The cheaper ones are 70-80). Higher the ppi greater the resolution - but - the same ppi over a larger length is worse. E.g., 100 ppi on a 32" panel is better than 100ppi on a 50" panel - at the same viewing distance - since the resolution of both panels is the same (1920x1080). What this means is that the pixel size increases as you increase the panel size. So if you're displaying text and fine-detail, you are better off with a bunch of smaller 32" panels than lesser 50" panels.

For general large displays, projectors are used instead of video walls - a full HD/2K projector is more than sufficient for large screens at 15+ feet or so, in a darkened environment. When video walls are used, the viewing distance is in the 'billboard' range (more than 30 feet). The use of consumer LED/LCD video walls over short viewing distances isn't a great idea, since they don't offer many advantages (but many disadvantages). So you have three options, assuming your display size is fixed:

1. Viewing distance smaller than 12.5 feet but no text or details on screen - I call this the 'grey' area.
2. Viewing distance smaller than 12.5 feet but text and/or details on screen
3. Viewing distance greater than 12.5 feet

If your case fits option 3 (as it should under most conditions, considering your screen size), then go with a projector and save yourself time and money.

If your case fits in with options 1 or 2, then you are better off with smaller panels with the same resolution. E.g., you can cover roughly the same area but have much better resolution with 17" panels in a 9x6 array. The total ppi for both sizes are as follows:
a. 50" - 43 ppi
b. 17" - 130 ppi - this will allow the people to read stuff at 2 feet

Obviously the big issue to consider is that if you have a 9x6 array, that's 54 connections with a total resolution of 17280x6480 - but that's what it takes for this particular case. You see where this is going, right? Combine all this with the fact that the best video you can shoot is only 4K, and you have a situation that most professionals consider video hell. You could just split up one HD signal over a 2x3 array - but please do the math on the kind of experience that will provide. It's not difficult to split a 5K image into 6 HD boxes - that would definitely be the way I would go.

If for some strange reason you still want to persist with a video wall, then what you need is a video wall controller. There are two kinds:
1. Hardware based
2. Software based

The decision you take will be based on the amount of displays you need to drive, the computing power available, the level of synchronization required, the resolution of your display, technical manpower available and budget. Unfortunately this can only be decided on a case-by-case basis. Search for video wall controllers, and speak to the companies directly.

Hope this helps, and all the best with your project.

[Scott Wilkinson]

Thanks Sareesh---great info!

I've continued grasping at production specs for our video array. And while I've learned a lot, I've also learned that the current technology for video arrays (multiple displays used as one) is lagging severely.

For example, the video array we'll be using at a large trade show in DC is 1x4...or an aspect ratio of 64x9. (Yep, definitely non-standard!)

You would think that producing video for this would be simple: the combined pixel dimensions of four 1080p displays in a row is 7680x1080. So you'd produce a video at one-half or one-quarter of this dimension, have the hardware send it to all 4 displays (scaling it as necessary), and you're done. Easy-peasy.

BUT...it doesn't work like this. My understanding is that there is no hardware that will do this. So then you must go down the rabbit-hole of squeezing, stretching, and formatting for larger, "imaginary" displays (in which your ACTUAL array is just 25%, in our case). In other words, design media at 1920x270 (which is 25% of a 16:9 frame), then drop this into a 1920x1080 project (in After Effects) and output that. (And I'm still not sure what will get stretched and how???)

Combine this with the question of how the array is being driven (computer? Blu-ray DVD?) and the question of whether you feed it a 1080p signal or a 720p signal...things can get very complicated. (Or at least that's how they seem to me.) And of course everything Sareesh said above. :-)

I've certainly learned that if your video array is NOT 16:9, it's going to be a pain...and there is no "one right way" to produce your media.

[Seth Bloombaum]

If your multi-display system is not of standard aspect ratio, you should look into Dataton's Watchout for flexibility in programming. Licenses aren't cheap, but, you can create just about anything you can imagine.

[Eric Olson]

Originally Posted by Scott Wilkinson

you must go down the rabbit-hole of squeezing, stretching, and formatting for larger, "imaginary" displays (in which your ACTUAL array is just 25%, in our case). In other words, design media at 1920x270 (which is 25% of a 16:9 frame)

Don't do it like that. Edit as 3840x540 and then master a 1920x1080 file in which the top half is the left two displays and the bottom half is the right two displays. Then your hardware can feed the 1x4 array as if it were a 2x2 array even though it is really a 1x4 array.

[Scott Wilkinson]

Hmm...that's interesting Eric. But can any hardware do this?

What the guy who's handling the setup told me was vague: something along the lines of "the video output—which can be HD—will be distributed to 4 processors, one for each monitor." That's about all he could tell me, LOL (no, he doesn't know much about this).

But your idea sounds interesting—I'm going to look into it.

Scott

[Sareesh Sudhakaran]

Originally Posted by Scott Wilkinson

For example, the video array we'll be using at a large trade show in DC is 1x4...or an aspect ratio of 64x9. (Yep, definitely non-standard!)

You would think that producing video for this would be simple: the combined pixel dimensions of four 1080p displays in a row is 7680x1080. So you'd produce a video at one-half or one-quarter of this dimension, have the hardware send it to all 4 displays (scaling it as necessary), and you're done. Easy-peasy.

BUT...it doesn't work like this. My understanding is that there is no hardware that will do this. So then you must go down the rabbit-hole of squeezing, stretching, and formatting for larger, "imaginary" displays (in which your ACTUAL array is just 25%, in our case). In other words, design media at 1920x270 (which is 25% of a 16:9 frame), then drop this into a 1920x1080 project (in After Effects) and output that. (And I'm still not sure what will get stretched and how???)

A complete standardized process for 1080+ resolutions isn't available. Even though there are 2K and 4K "systems", there isn't a camera-to-screen standard specified by SMPTE yet. The best we have is HDSDI.

The out of the box solution for 1x4? Shoot four 1080 genlocked cameras side by side - parallax and gaps will go unnoticed because you are using panels with borders. You could also slightly converge the cameras and correct on set. This workflow is carried out everyday by channels covering live broadcast events. The only difference is that the cameras are at different vantage points. The signals are genlocked and switched on the go.

Here's a sample workflow, the cheapest I could think of, without compromising on resolution:

• 4x Canon XF105 outputting HD-SDI video (or capture to CF cards and ingest), genlocked. Use this for HDSDI: NVIDIA Quadro Digital Video Pipeline

• Edit using only one (or two videos) of the four streams - i.e. one 1080 project - no sense compounding the problem at this stage - but you must organize your footage carefully.

• When edit is locked and finished, output each stream to its own file - 4 rendered files. You can round trip to AE and back to your NLE easily if working with Premiere.

• Each 1080 file/stream can be played back via 2x dual SDI/HDMI outputs, frame locked using the Nvidia interface.

• If you have enough computing power, you can attempt to run all four streams in one 7K custom project but why do it if you have to separate it again? How are you going to transmit a 7K video with prosumer/consumer equipment anyway?

This solution is tricky for 2x3 or higher, but not impossible. The "advantages" are that you have full resolution, easily manageable data streams and a prosumer solution that can be scaled according to need. The "disadvantages" are getting the footage to sync, it's still not cheap, getting each stream to look the same, and the need to reconfigure for every project.

If your display is on a trade stand, then the average viewing distance is 3 to 10 feet, especially if your unit faces the walkway. Shooting a single 1080 video and scaling+cropping it 4x is going to give very poor results. Try watching an SD broadcast on a 55" monitor at 3 feet and you'll get a rough idea. Finding the right location for the display is part of the workflow.