The term ‘plug
and play’ has been around for decades and mostly pertains to the ease of use of
technology systems. It’s especially appealing to non-technical consumers prior
to opening the box of a new technology-related product. But, at least for the
AV professional, it’s often a different story. Video communication
is literally stealing the show in the modern age - from marketing platforms to information
management and entertainment. For the viewer, it’s as simple as pressing a button
and selecting what to watch, or even watching whatever is already displayed. The
intricate part, however, is delivering the content from the source to the
screen – a process unseen by the user. This has been the cause of many a grey
hair for the AV professional. Video distribution has its limitations, which
need to be known when designing signal distribution systems. As technology
develops, new signal types also come with new challenges.
The most common
signal type used in current day video is HDMI (High Definition Digital Media Interface) because of its diverse design. With the introduction of
high definition satellite television to the residential market, digital video connection
between source and screen was done with HDMI. It was a simple, fresh and
effective new component that arrived with the whole new world of high definition
television. In fact, HDMI was developed to carry a variety of signals in a
single cable. This primarily includes a video component, which is capable of
transporting video signals in extremely high resolutions, and an embedded
digital audio signal that delivers adequate audio information for the most
recent surround sound variants. These two components are sufficient to deliver
a comprehensible video signal, but HDMI technology exceeds this by far and
additional information is available on the same cable infrastructure
Thus, over and
above the audiovisual components, HDMI 1.4 includes an Ethernet channel, enabling
high-speed, bi-directional network connectivity at up to 100 Mbps. Display
resolution is recognised with EDID (Extended
Display Identification Data), which
is available to identify the native resolution of a display as soon as it is
connected to a video source. The source component will respond by transmitting
the content in the optimum resolution that the screen is capable of receiving.
In most cases it will be full HD (1920x1080) or, these days, even UHD
(3840x2160). Challenges include, for example, sending a full HD signal to a
WXGA projector with a native resolution of only 1280x800 – which would be incapable
of displaying the complete pixel space of the source image. In this scenario,
one of two adjustments can be made to display the content. Ideally, the display
device would scan convert (downscale) the image to match its own native resolution.
If this is not possible, the source device would reduce its own output
resolution in order to meet the display. The latter is not ideal for networked
video distribution systems, as the source content’s quality would then be
reduced on all connected displays - regardless of their capability to meet a
higher definition video.
HDCP (High Bandwidth Digital Content Protection) is the main element behind
the development of HDMI as a standard video format. For decades, Hollywood
producers have been fighting the piracy war in spite of content duplication
being legally prohibited. It has always been a losing battle as there is no effective
way to prevent consumers from duplicating analogue video. In a digital world, many
parameters can be introduced to a signal to only allow duplication when certain
criteria are met. HDCP did exactly that by creating a standard that couldn’t be
legally duplicated unless all components in the particular system conforms to a
licensed process. Law enforcement is much easier when all stakeholders in the
video supply chain are forced to conform, instead of just the end consumer. HDMI’s
trump card is that the source component will not transmit a video signal unless
a digital handshake takes place to confirm that the display device is licensed
as well. Recording equipment will not tick all the required boxes and hence
remain unlicensed. A source device will thus not release a video signal
connected to a recording device. In layman’s terms, HDCP prevents the digital
signal flow unless the display device is HDCP compliant. With economic
pressure, the manufacturers of video players and displays are very eager to
license their products to avoid paying the price of non-compatibility. Unfortunately,
there will always be electronic devices on the black market that override these
parameters.
CEC (Consumer
Electronics Control) is another feature of HDMI which enables users to control
multiple connected devices with a single control interface. A DVD player, for
example, can be controlled via the connected HDMI feed, or a third-party
control system can control sources and display devices from a single user
interface. With all the
above components forming part of the HDMI signal, bandwidth requirements are clearly
extensive and, as a result, distribution distances are limited. A full HD
signal should not be distributed farther than 15m. In a standard residential
dwelling this will be adequate, but in larger residences and in professional
systems especially, the distribution becomes a challenge. Cables are available
at lengths of up to 22m and will work well with lower resolutions, but this might
be problematic as the bandwidth increases. In these larger systems even 22m cables
won’t be adequate to distribute signals to all displays.
With these
distance limitations, an entire new world of opportunities has opened up. Many
technologies are available to distribute HDMI - each with unique architecture
and challenges. There are balun transmitter- and receiver sets that distribute
the HDMI signal components over twisted pair cables, and HDBaseT that uses the
same infrastructure but also transmits additional signals such as control
protocols and even low voltage power supply on the same cable. Fibre optic
mediums are positioning themselves amongst these technologies and, although
expensive, are capable of transmitting digital signals across longer distances.
The latest technology
breakthrough to see the light is based on the IP infrastructure available in everyday
IT networks. These two technologies are encroaching on the other’s territory as
they improve. The challenge has always been that the available bandwidth in
current day networks is far too little for the vast number of data packets of a
video signal. Many compression techniques bridge the gaps and higher bandwidth networks
are available, but the latter adds an extra zero to the price tag. Despite all
these red flags, Video over IP technology adds a fresh new dynamic to video
distribution systems by replacing the conventional video router or switcher with
a network switch. True to IT network architecture, video inputs and outputs can
be connected at any patch point across the network and routing takes place
based on IP addresses. Because video signals can be distributed as IP packets,
wireless systems are also seeing the light of day - but many creases still need
to be ironed out. It will happen eventually, it’s just not possible to say
exactly when.
Video
distribution, from small to large systems, may have given consultants and
technicians many a headache in this exciting industry. But, luckily, almost
always with a happy ending.
