COBHAM H264ENC Guia do Utilizador descarregar pdf (Página 106)

SOLH264TX Broadcast Transmitter

H264TX, H264ENGTX, H264ENC

UNCLASSIFIED

Part A - User Guide

DS000091

Rev 1.2 2013-05-02

UNCLASSIFIED

Page 13-96

13.6 About Program Number

Transport stream has a concept of programs. Each single program is described by a

Program Map Table (PMT) which has a unique PID, and the elementary streams

associated with that program have PIDs listed in the PMT.

For instance, a transport stream used in digital television might contain three programs, to

represent three television channels. Suppose each channel consists of one video stream, one

or two audio streams, and any necessary metadata. A receiver wishing to decode a particular

"channel" merely has to decode the payloads of each PID associated with its program. It can

discard the contents of all other PIDs.

13.7 The Relationship between PIDs, Program Number

and Chaining Number

We saw above that Cobham transmitters have a set of default PIDs which is fine if you are

sending just one program.

When we start chaining devices together to send multiple video programs over one RF link

for example, we need to identify those programs so that the receiver can decode them

separately.

We saw above that the Program Number is used to uniquely identify a ‘channel’ in a

Multiple Program Transport Stream (MPTS).

13.7.1 Chaining Numbers vs. Program Numbers

When we are setting up chaining we need to give each encoding device a separate

Chaining Number.

If you use the Chaining Number 0 for example,

zero

is added to the default PIDs and this

gives you Program Number 1.

If you use Chaining Number 5, five is added to the default PIDs and this gives you Program

Number 6.

A table makes it clear:

Chaining Number

Program Number

What happens to the Default PIDs?

Adds 0

Adds 1

Adds 2

Adds 3

Adds 4

Adds 5

Adds 6

1 2 ... 101 102 103 104 105 106 107 108 109 110 111 ... 124 125

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