2.4 MPEG-2 code stream multiplexing and Business Information
Audio and video and digital signal first through the MPEG-2 encoder data compression, through program multiplexing to form the basic code stream (es), the basic code stream after packaging to form a packet header of the basic code stream (PES ). PES streams representing different audio and video signals are sent to the DTs for system reuse. The reused code streams are called transmission streams (TS). transmission streams contain different signals from multiple program sources. To distinguish these signals, you need to add business information (SI) to the system multiplexing so that the receiver can identify different programs. To facilitate understanding of the service information of the DVB transmission system, we will give a rough introduction to the structure of the transmission code stream. The length of each transmission code stream data packet is defined as 188 bytes long, as shown in 1.
Figure 1
Figure 1 Structure of the transmission code stream
Figure 2
Figure 2 Structure and meaning of Baotou
Among the 32-bit data in Baotou, the 13-bit PID code is particularly important. It is the key to identify the nature of the code stream information and the "ID card" of program information ", different TV programs and Business Information (SI) pairs should have different PID codes. For a decoding receiver, in order to find the TV program it receives, it first finds the table corresponding to the Business Information (SI) through the PID code ), then, the business information table shows the PID code of the program to be received and the corresponding clock PCR to restore the program.
In addition to PSI (Program Specific information), Business Information (SI) mainly includes:
BAT: Bouquet Association Table, program Business Group Association Table
Nit: Network informatio table, network information table
SDT: service description table, program business description table
EIT: event information table, program segment information table
RST: running status table, running status table
TDT: time and date table, time and date table
TOT; Time Offset Table, Time Offset Table
St; stuffing table, fill table
Pat: Program allocation table, program Association Table
Cat: Conditional Access Table, conditional receiving table
PMT: Program Map Table, program ing table
The first four bytes of each transmitted stream data packet are headers. the header is followed by useful information to be transmitted, including audio, video, or data information, which is usually 184 bytes in length, sometimes an adaptation field is inserted into usefull data to supplement an incomplete transfer stream and place the decoding clock (PCR ). The header of the transmission stream is the key to identifying the transmission stream. Its size is 32 bits. Its structure and meaning are 2.
