Kevin Jackson /
01.01.2009 12:00 PM
Multiviewer evolution

The modern monitoring and control room environment has evolved greatly over the last 10 years. It has progressed from the traditional CRT-based monitor stack to the myriad of multiviewer solutions available today. There are several different approaches to monitoring. This article will discuss the three main options available to broadcasters today and the challenges each presents.

A little back story

The traditional approach to broadcast monitoring was to view each video channel on an individual CRT monitor. A signal was hardwired to a particular monitor, usually via a patch panel. The location of sources was rarely, if ever, changed. The only information available about a source was visible via an LED under monitor display (UMD). Prior to that, source information was merely printed on a label that was manually attached under the monitor. The monitor stack was large, inflexible and functionally limited.

As the digital revolution arrived and the number of channels, formats and delivery mechanisms increased, CRT monitor stacks were replaced by multiviewer-based solutions. As these technologies evolved, they provided broadcasters with the flexibility to reconfigure walls at the push of a button. They enabled broadcasters to add or remove channels, allocate greater wall space to critical feeds and reduce wall space for feeds of lesser importance.

Initially, broadcasters resisted the acceptance of LCD technology — mainly because of fears related to image quality. This apprehension has all but disappeared with the evolution of display technology. Flat-panel displays are now the norm. In the context of monitor walls, multiviewer and flat-panel displays offer great advantages in terms of the size, depth and weight of the monitor wall. They reduce air-conditioning requirements and save space because ancillary equipment — such as UMDs that indicate channel identities, on-air status lamps and studio clocks — can be virtualized by the multiviewer.

This virtualization allows broadcasters to incorporate a multitude of monitoring functions alongside the video display, while providing a flexible, reconfigurable interface to the operator. The ability to reconstruct the wall at will, change layouts, and receive dynamically updated status information and automatic fault notification have quickly become vital functions for broadcasters. Signal integrity measurements and data monitoring can now be found in the multiviewer, and their status can be recalled to the monitor wall by the operator at the touch of a button. Audio metering, channel IDs and tally status information — once displayed on separate devices within the control room — are now routinely routed to the video wall.

Traditional approach

The first generation of multiviewers were simple screen splitters. A certain number of sources were received and evenly split on a single display. For example, an early 16-input splitter might only have provided a simple 4 × 4 arrangement to a single display. However, the ability to edit layout arrangements, drive multiple displays (at increasing resolutions) and accept multiple video formats soon became key requirements.

The architecture of those early screen splitters is still in use today in modern multiviewers. Video sources are fed into a studio router, whether they are live camera sources in a production environment, or satellite or cable feeds in a transmission or master control facility. From here, sources are routed to the multiviewer to be viewed on the monitor wall. In this architecture, a section of router outputs is dedicated to supplying the multiviewers. (See Figure 1) This design has the advantage of being reasonably flexible, as the router can select any of its inputs to be routed to any or all of the inputs on the multiviewer.

It also has advantages in terms of redundancy from a system point of view. Using several different multiviewers reduces the chance of complete system failure, as it is more unlikely that a chain of discrete multiviewers would fail than it would be for a single device to fail. It is also an inherently scalable solution, as it is quite easy to increase the monitoring capability of such a setup. Additional multiviewers can be added as necessary and connected into the system, provided there are enough outputs available from the router.

However, this type of setup has some disadvantages. The choice of multiviewer and router must be carefully made to ensure control compatibility. Depending on the combination, it may or may not be possible for the multiviewers to switch the upstream router.

Additionally, in a production environment, UMD and tally status information are always key concerns. The system designer must consider how to pass this information from the router through the multiviewer to provide on-screen indicators. The system designer should also consider which protocols and what physical communications means (normally RS-422 or TCP/IP) will be employed, as well as the associated cabling requirements.

In this type of architecture, it can be advantageous to use external UMD and tally controllers to translate to different devices, especially when the broadcaster is using equipment from different vendors. A key consideration in this type of setup is the amount of dedicated rack space that may be required if the system grows exponentially. Other considerations include the cabling and control for configuration, switching and UMD/tally status that are needed between the router, the multiviewer and the display.

The discrete multiviewer approach provides greater levels of redundancy and is inherently scalable, which is why it is typically favored for midsized monitoring facilities with a growth path planned for the future. For operations that require a large number of displays — especially if these displays carry out different functions or are used by different operators — this approach is often the most suitable.

As illustrated in Figure 1, the multiviewer in broadcast monitoring traditionally sits between the router and the display. However, in the last two years, integrated router and display solutions have emerged.

Routers with integrated multiviewers

This traditional architecture (router to multiviewer to display) opened the way for alternative approaches as other equipment has absorbed the multiviewer functionality.

One approach integrates the multiviewer functionality within the router, which removes the necessity for external cabling and additional rack space, and simplifies control. (See Figure 2.) When the multiviewer is contained within the router, it has easy access to the router crosspoint control. Simple and complex switching arrangements — such as placing any router input onto any display — are easy. Additional functions, such as the ability to sequence through all or a group of inputs — for example, scrolling through all of the router inputs for occasional confidence monitoring of lower priority sources — are simplified.

A key consideration with such anapproach is the lack of access to the multiviewer input signals, as all the routing is internal. In the basic architecture previously described, it is possible to place a distribution amplifier (DA) between the router and the multiviewer if the signals are needed further downstream. For example, in production, the program feed is transferred to the multiviewer for monitoring and is also forwarded on to transmission.

With the integrated solution described above, however, the same signal will need to be switched to additional router outputs in order to make these signals accessible at other points on the broadcast chain. Furthermore, integrated multiviewers only offer a limited, fixed number of display outputs per group of inputs — for example, 32 inputs over four displays. If another display is needed, an additional multiviewer module would be required. This could add significant cost and result in further loss of direct router outputs.

These types of architectures also involve a slight increase in risk, as all routing and monitoring are contained within a single chassis. However, because routers are usually designed to provide the highest level of reliability (redundancy is built-in for all vital components), this risk should not cause potential users to refrain from considering this solution. The router with an integrated multiviewer offers a highly compact, powerful alternative to the traditional design and is gaining acceptance throughout the industry.

The integrated approach can be particularly well-suited for large master control rooms, as it enables greater flexibility and easy control, and the greater scale offsets the large initial investment in capital equipment and space.

Space-saving monitors with integrated multiviewers

For situations in which space saving is a primary requirement, an alternative multiviewer solution has recently emerged. Manufacturers are now integrating multiviewer capabilities within the display. Displays with multiple video inputs are becoming increasingly popular in the broadcast environment. (See Figure 3.)

As some of these solutions are in their infancy, the specifications of each should be carefully examined to ensure a full range of broadcast features are offered. These include UMD and tally support, flexible layout capabilities and extended monitoring (such as embedded audio decoding and display and ancillary data decoding).

Integrated multiviewer displays are becoming especially successful in the OB production environment, which places emphasis on pristine image quality and low system latency. These environments frequently favor a small number of sources per display (typically a quad-split). Because an OB environment often includes a large number of displays with a low number of sources per display, an integrated router solution could be quite costly. External multiviewer solutions can be used in such an environment, because they are inherently scalable. The integrated multiviewer display offers this scalability while removing the requirement for extra rack space.

These displays also eliminate the need to consider the distance between multiviewer and display. Typically a DVI link is limited to 5m unless an extension is used. Integrated multiviewer displays have a limited number of inputs and therefore do not have the flexibility of discrete multiviewers. A quad-split display by nature cannot display more than four sources at any one time. But depending on the requirements of the broadcaster, the advantages of this compact solution often outweigh the limitations.

Conclusion

Each monitoring approach has its own merits with respect to cost, size and complexity. The system architect must weigh all factors to find the solution that is best suited for a particular environment. The broadcaster should carefully consider its present and future system requirements before making an investment. The optimal monitoring solution ultimately depends on factors such as cost, space, redundancy and flexibility. Working with a vendor that offers a full range of options can help guide the system architect in deciding upon the best solution for a particular application.


Kevin Jackson is product manager, multiviewers, for Harris Broadcast Communications.



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