In the first part of this series, we learned to understand why video wall controllers are such an important part of designing any video wall project, be they LCD displays, projectors or direct-view LED. Today, we’ll pick-up where we left off, by examining the most complex type of video wall content, where we have two or more source images spread across the video wall, where one or more of those source images spans across multiple display devices.

These kinds of video walls are prevalent in command and control

environments, in high-end meeting and conference spaces, and most recently,in more and more classrooms and training facilities. They are also very commonly used as video billboards in digital signage applications, where many composite images or videos can be artistically arranged to present an image to the viewer.
Video Wall
These types of video walls can easily be equipped with interactive capability to allow the presenter, viewer or trainer to manipulate the images via touch. There can be a lot going on here, and it all can be done with a single video wall controller. In fact, multiple video walls can be controlled in this way from a single video wall controller. It’s all possible, but the first order of business is to determine the total number of input sources and the total number of output display devices that will make up the system.
First, we must come to an understanding about video resolution. Today, everybody wants 4K UHD televisions, right? That’s fine for a single display. Now, when you put multiple displays together to make a video wall, you need to account for how the source content will appear on that expanded canvas of the video wall. As an example, a 2x2 video wall made up of four 1920x1080 displays makes a canvas resolution of 3840x2160, the same as a 4K UHD display. If you have a 3x3 video wall made up of nine 1080p displays, you end up with a 5760x3240 resolution. Even if your source content is 4K UHD, it is not enough to fill all the pixels of a 3x3 video wall. So, upscaling needs to occur.

If you use 4K UHD displays in your video wall, you will have exceeded the resolution of your 4K UHD source content at even the modest 2x2 video wall. This requires upscaling, and even with an exceptional scaling engine, you will quickly exceed the ability of the scaler to properly interpolate all the pixels without the introduction of video artifacts. So, 4K UHD displays are a waste of money in any video wall beyond maybe a 2x2. If source resolutions become 8K and beyond, we might be able to reevaluate this conclusion. For now, we use 1080p displays for video walls.

Next, we need to understand what it takes to be able to process and manipulate such large numbers of pixels. Even in a modest 2x2 video wall made up of 1080p/60fps displays, we have to deal with 8,294,400 pixels, sixty times every second. That’s 497,664,000 processes every second. To be able to do half-a-billion processes every second, requires some serious computing power.

Most video wall processors are dedicated PCs, most of which are running Windows (some run Linux). Every PC that runs such an operating system also has “overhead” running the usual tasks, such as network communication, peripheral management, memory allocation and the like. So, running all these tasks along with all these processes introduces a substantial amount of latency. That’s the delay between source input and display output. In many cases this can be measured in seconds of delay. One way of reducing this latency is to reduce the complexity of the video processing. However, that reduces the quality of the output images significantly. Another way of reducing latency, is to off load processing to capture cards and graphics cards, lightening the load on the CPU. Further reduction in latency can be achieved by designing a dedicated hardware-based processing appliance that runs no operating system, uses no task overhead, and contains ASIC processing chips that do only one thing – process the desired video signal. With this kind of design, latency can be reduced to <10ms, unseen by the human eye.

Taking this information into consideration, let’s design a practical video wall with multiple 1920x1080 LCD displays.

In this example, let’s say we are designing a command and control center with 24 displays configured 3-high by 8-wide across the front of the control room. We have eight video feeds from cameras and four data feeds from PCs. So, we’ll need twelve inputs and twenty-four outputs. The application requires that the layout of the video wall will change depending upon the situation, so we’ll have to be able to control switching sources and video wall layouts easily. They requested wireless tablet control to do that, as well as the ability to see the content on the video walls, on the tablet or PC, as they are switching layouts.

Diagram One
As you can see from the drawing, one video wall controller can handle all of the required tasks for this example project. We simply equip a chassis with the twenty-four HDMI outputs with six output cards, one IP input card for the eight IP cameras, one four-channel HDMI input card for the PCs, and one network preview card that allows streaming preview and control over the wireless network.

The video wall controller used in this example is the Digibird VWC2, which is a hardware-based video wall controller, with a video latency of less than 10 milliseconds. This is accomplished using a new generation of FPGA chip technology. As we discussed earlier, this is a dedicated hardware platform, so no off-the-shelf OS is being used. The advantages are clearly the ultra-low latency performance and the artifact-free video processing. The disadvantages of this type of hardware system is that you cannot run any applications on the controller. So, for interactive and conferencing applications, this type of controller may be less preferable than a Windows-based controller that allows you to run your web conferencing software, or interactive collaboration software right on the controller.

In our next installment, we’ll look at an edge-blended projection video wall solution and then expand that to include an LCD video wall for overflow.