These kinds of video walls are prevalent in command and control
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.
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.