Streaming - A Practical Guide to Video and Audio Compression - page 357

With an open-source streaming server, the licensing issue may be less of a problem.
But there you run into a capacity problem. Soon, your traffic levels exceed the bandwidth
that you have purchased from your ISP. You may have a very happy relationship with
your ISP, and as long as they are warned in advance, they may allow your service to burst
to multiples of your normal total outgoing bit rate and not charge you a great deal of
money. On the other hand, they might require that you purchase additional bandwidth to
cover the expected overload. Be careful not to purchase a service level that has capacity for
your high-traffic times when the average traffic levels never reach this most of the time. If
your traffic is “bursty,” it's a good idea to work out a deal based on bandwidth actually
used rather than budgeted capacity that may be underutilized.

20.9 Streaming to Large Audiences

Distributing video to large numbers of people over broadband connections is growing
very quickly as an industry. Now that codecs are efficient enough to deliver good-quality
video at about 1.2 Mbps and reasonable quality at 800 Kbps, broadband comes into its
own. That is not to say that broadcast TV will ever go away. Broadcasting has some com-
pelling advantages compared with the uni-casting approach of a streaming service, such
as the way you can broadcast just one copy of a program and everyone receive it at once.
Building video-on-demand services with a broadcasting system that lacks a return path
and only has one outgoing stream is impossible. Some interactive, multi-stream services
have been rolled out and are successful, but that isn't truly video on demand.

20.9.1 Uni-Casting

Uni-casting is a technique in which a client makes a connection to a media streaming serv-
ice and the server delivers an individualized bit stream. This is how Internet video stream-
ing used to be done in the very earliest implementations, and it is truly a video-on-demand
model. You get exactly the content you requested, and you have it delivered at the time you
request it. Someone else may request that same content only a second later, or even at the
same time, but he or she will get a separate and individually delivered bit stream with no
relationship to yours. The uni-casting model is illustrated in Figure 20-4.

Server process One client

Server process One client

Server process One client

Server process One client

Figure 20-4 Uni-casting model.