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systems for live
events What makes wireless camera systems a viable
option now as opposed to only a few years ago?
When the COFDM modulation scheme was introduced over a decade ago, it
revolutionised event coverage and newsgathering. It meant that digital wireless
camera systems could be used for the first time to transmit non-line-of-sight
digital signals, which gave producers complete freedom to go live from locations
that were previously out of the question with wired systems.
However, it’s fair to say that early versions of such systems had drawbacks,
which meant that the uptake got off to a staged and somewhat troubled start.
Although MPEG-2 served the wireless camera industry adequately for a number
of years, the introduction of HD and its vastly increased bit rates put a lot of
pressure on the availability of RF spectrum, which was already stretched. Some
began to question whether going wireless was actually worthwhile.
Then along came H.264 encoding, which prompted users to take another look
at whether H.264 encoding was, or could be made, viable for wireless camera
systems. In their earliest manifestations, H.264 encoders were considered too
large and power-hungry to be useful for wireless cameras.
However, like most technology advances that loosely follow a corollary of
Moore’s law, encoders soon became far more compact yet more reliable and
required less power, using as little as 10W. (If I may, we recently introduced a
mini HD transmitter – the worlds smallest – that consumes only 7 watts!)
Problem solved, then?
experts At the time, not quite. The resolution of the size and power questions still left
concerns over latency, which was a major issue with early versions of H.264
encoders. Such systems typically had latencies in excess of 500ms, which
was wholly unacceptable for large multi-camera events because it caused
very noticeable lip-sync issues when mixing cabled and wireless cameras. This
problem was particularly acute for newsgathering applications because the
addition of encoding delays on top of those already present in an SNG encoder
and satellite hop made live two-ways very difficult. Fortunately, in the last few
years, new encoding techniques have dropped latency to below 100ms, which
has not only made H.264 encoding a viable option for wireless communication,
but a preferred one.
Are all H.264 systems pretty much the same?
Stuart Brown, Broadcast Systems
Director, Cobham Broadcast
58 | TV-BAY MAGAZINE: ISSUE 81 SEPTEMBER 2013
Not necessarily. While H.264 encoding for wireless systems has been widely
adopted, it has to be said that not all H.264 encoders are created equal. It’s
relatively easy to make exaggerated claims about latency and/or encoding
efficiency – often citing the encoder’s response to test patterns as ‘proof’, only
for the user to discover, too often during a live shoot, that the picture quality/
encoding efficiency they were meant to achieve came nowhere near the stated
claims when the system is used with ‘real’ pictures. There have been
instances in which a deployed H.264 system had to operate at MPEG-2