Digital Television - A Practical Guide to Video and Audio Compression - page 429

27.2 The Set-Top Box

In the United Kingdom and elsewhere that the DVB standards are deployed, the MPEG-2
codec is used for video coding. This is embedded in silicon so that receivers can be built
inexpensively. The carriage occurs via a transport stream that multiplexes several channels
together into a single bit stream.

27.2.1 DSP Technology in Set-Top Boxes

Here is a possible alternative strategy that revolves around developing set-top boxes with
video digital-signal processors (DSP) instead of application-specific integrated circuits
(ASIC) containing the codec. The DSP can be loaded with a replacement codec on the fly,
but ASICs are hardwired when they are manufactured. Texas Instruments has demon-
strated that the codec could be delivered as a header on the front of the program and then
loaded into the DSP when needed. That requires a closed system to work effectively. This
is an attractive solution for box manufacturers who are uncertain whether to deploy the
VC-1 (Windows Media) or the H.264 codec in the short term. The codec is swapped in the
field by reloading the DSP chips with the new software.
Equator Technologies and Hitachi Semiconductor are demonstrating similar experimen-
tal work. Many other companies are also working in this technology area. These DSP chips are
designed for real-time processing with algorithms as complex as that described by H.264.

27.2.2 H.264 on TV Set-Top Boxes

Rolling out H.264 compatible coders and set-top boxes is no small challenge. In the United
Kingdom there are in the region of 10 million MPEG-2 boxes in consumer households.
These devices are not going to be replaced quickly.
Upgrading the firmware is not a viable solution because the computing overhead for
decoding H.264 compatible and the necessary memory is more than these boxes have
available. This legacy situation comes about through delivery of free boxes to the con-
sumers with the hope that the subscription revenues over several years would pay off the
cost of the box. Those with the deepest pockets achieved the largest market penetration.
So, in the United Kingdom at least, no one is in a hurry to replace the receivers.

27.2.3 HDTV

New markets for TV services have the advantage that they have no installed base and so
a new standard is a viable option.

Electronics Weekly DSP special issue: http://www.electronicsweekly.com/Issue200.htm
EDN DSP companies listing: http://www.ednasia.com/dsp2003.htm
Hitachi Semiconductor: http://www.hitachisemiconductor.com/
Texas Instruments: http://www.dspvillage.com/
Equator Technologies: http://www.equator.com/