The MPEG Data Stream - Digital Video and Audio Broadcasting Technology - page 37

number of camera angles (track, spectators, car, helicopter) and presented
in different languages. All the multiplexed data streams of all the programs
are then multiplexed again and combined to form a complete data stream
which is called an “MPEG-2 transport stream” (TS for short).

Video1 Program 1

PID=0x200

Encoder

PID=0x300

Audio1

Video2 Program 2

Encoder

MPEG2 TS

Audio2

Video3 Program 3

PID=0x100

Encoder

PID = Packet identifier

Audio3

Fig. 3.7. Multiplexed MPEG-2 transport stream packets

An MPEG-2 transport stream contains the 188-byte-long transport
stream packets of all programs with all their video, audio and data signals.
Depending on the data rates, packets of one or the other elementary
streams will occur more or less frequently in the MPEG-2 transport
stream. For each program there is one MPEG encoder which encodes all
elementary streams, generates a PES structure and then packetizes these
PES packets into transport stream packets. The data rate for each program
is usually approx. 2 - 7 Mbit/s but the aggregate data rate for video, audio
and data can be constant or vary in accordance with the program content at
the time. This is then called “statistical multiplex”. The transport streams
of all the programs are then combined in a multiplexed MPEG-2 data
stream to form one overall transport stream (Fig. 3.7.) which can then have
a data rate of up to about 40 Mbit/s. There are often up to 6, 8 or 10 or
even 20 programs in one transport stream. The data rates can vary during
the transmission but the overall data rate has to remain constant. A pro-
gram can contain video and audio, only audio (audio broadcast) or only
data, and the structure is thus flexible and can also change during the trans-
mission. To be able to determine the current structure of the transport