Streaming - A Practical Guide to Video and Audio Compression - page 350

20.5.2 MPEG-4 Fine Grain Scalable Profile

The MPEG-4 Fine Grain Scalable (FGS) profile is well suited to streaming situations
because it is designed to be resilient to the way that available bit rate changes in capacity
during a session. The available bit rate might decrease to almost nothing and then sud-
denly burst at full capacity again. The FGS profile allows the encoder to build a very low
bit-rate foundation video stream and then deliver an optional enhancement layer. The
minimal bit-rate situation allows the base level through but the enhancements can be dis-
carded. Thus, a minimum level of performance is maintained while allowing better-qual-
ity video to be delivered when the bit rate is in plentiful supply again.

20.6 Multi-Stream Embedding and Multiplexing

The services delivered to the client user need to combine many separate streams of infor-
mation. Figure 20-1 is a diagram showing the way that streams are nested together.

20.7 Streaming Servers

These are something of a commodity application now. Originally, there was a market for
streaming servers that could generate significant revenue streams for a company. Real
Networks made some useful capital from it in the 1990s. However, the free and subsidized
Windows Media content servers mortally wounded this business model. The coup de
grace was delivered by the open-source Darwin Streaming server. Real Networks
responded by making the Helix project open source and hence freely available.

Elementary video stream

Video Video Video Video

Programme stream

V A D V A D V A D

Elementary video stream

Audio Audio Audio Audio

Interactive data stream

Data Data Data Data

Figure 20-1 Packets and streams.

Darwin server: http://developer.apple.com/darwin/projects/streaming/
Darwin home page: http://developer.apple.com/darwin/
Helix server: https://helixcommunity.org/
Windows Media servers: http://www.microsoft.com/windows/windowsmedia/9series/server.aspx
QuickTime Streaming Server: http://www.apple.com/quicktime/products/qtss/
Live Channel streaming service: http://www.channelstorm.com/