Smart Buildings Systems for Architects, Owners and Builders

nine variations of EDTV dealing with the number and shape of pixels, as

well as the aspect ratio.

High Definition (HDTV)—HDTV offers the highest-quality resolution and
uses a 16:9 widescreen aspect ratio only. HDTV has six variations addres-
sing lines of resolution, number of pixels, frame rates, and interlacing.

Digital Video Transmitted via a Data Network

If one were to digitize the traditional analog video signal, assuming that each
pixel needed 3 bytes of information to indicate color, the digital signal would
need a transmission rate of over 8 Mbps, a high-bandwidth network require-
ment that is still beyond the capability of the vast majority of data networks.
To reduce the size of digital video several techniques were deployed; the num-
ber of frames per second was decreased, the sizes of screens were reduced,
transmission for pixels that did not change frame to frame were eliminated,
compression techniques were used and so forth.
The result was the development of hardware or software codecs (coding and
decoding devices) that compressed analog video and decompressed digital
video signals. Codecs were developed around a series of compression stan-
dards such as the H320 and H323 standards.
Video can be digitized in several formats but typically uses an MPEG
(Motion Pictures Expert Group) standard for the encoding and compression
of digital multimedia content. MPEG-2, or its latest incarnation, H.264, pro-
vides compression support for the TV-quality transmission of digital video.
Other standards address channel change signaling and video on demand.
Delivery of video over a standard data network can be performed in several
modes:

n Multicast Mode—programming can be sent to multiple devices at the

same time

n Unicast Mode—programming can be sent to just one device

n Broadcast Mode—programming can be sent to all open devices at the

same time

A typical deployment of video distribution (Fig. 8.2) in a smart building
involves:

n Digital television transmitted over a TCP/IP-based data network

n Digital video distribution that transmits and receives MPEG video streams

94 Smart Building Systems for Architects, Owners, and Builders