Guide to business information and electronic programs in the DVB code stream

How to quickly find the programs required by users in many digital TV programs, it is a problem to be solved in digital TV applications. In DVB generally, electronic program guides are used in receivers ( EPG ) this tool allows you to quickly find programs and generate EPG the data source is DVB business information in the code stream Si information.

on a digital TV, all the video, audio, text, images and other digital processing has become the data, and according to the MPEG-2 Standard packaging, forming a fixed length ( 188 bytes) Transfer package, then these data packets are reused to form a transfer code stream ( TS ), generally, a channel corresponds to a TS stream, TS streams of a single channel are composed of multiple programs and businesses. In TS if no boot information is found in the stream, the terminal device of the digital TV cannot find the desired code stream, therefore, in the MPEG-2 , the PSI information, which is used to automatically set and guide the receiver for decoding. PSI information is inserted to TS stream, identified by a specific PID (package identifier.

InMPEG-2Program information defined in the StandardPSIIs a description of a single code stream. Because the system usually has multiple code streams, in order to enable users to quickly find the services they need in multiple code streamsDVBPairMPEG-2OfPSIInPSINine more tables are added to form the four tables.Si.SiIt is a description of all the code streams of the entire system. It describes the system transmission content, broadcast data stream orchestration, and timetable. It includesPSIInformation.

I. Program Information (PSI)

PSIAssociate a program table (Pat), Conditional receiving table (Cat), Program ing table (PMTAnd network information table (NIT), These tables are insertedTS.PSISpecifies how to correctly find a specific program from a transfer stream carrying multiple programs. When the receiver wants to receive a specified program, it first obtains the program ing table of the program from the program Association table.PIDValue, and thenTSFindPIDThe program ing table corresponding to the value. The program ing table obtains the basic code stream that constitutes the program.PIDValue.PIDThe value filters out the corresponding video, audio, data, and other basic code streams. After decoding, the codes are restored to the original signal and the remaining data streams are deleted.PID.MPEG-2Structure of the Transfer Stream1.

 

Figure2YesPatAndPMT.

 

Figure3YesCatAndNIT.

 

As shown in the preceding figure, to ensure that the stream can be normally received, there must be at least one complete and effective stream.Pat.CatDescribes the program encryption method, which includes the program'sEmmRecognitionPIDOnly authorized decoder canCatReceives the key and decodes the corresponding data stream.NITIt contains information about the channel tuning parameters, frequency, and symbol rate of the program. This information allows the receiver to change the channel and tuning parameters with little or no delay according to the user's choice, correctly decodedTS. BecausePSIData integrity is very important, so in eachPSIThe verification code must be added to the CIDR block.

Ii. Business Information (Si)

PSIData only provides a singleTSSo that the receiver canTSBut it cannot provide multipleTSBusiness and program types, programs, start time, and so on.DVBSystem pairPSIExtended, providing a variety of other forms with different types of information to formSi. In practice, we willSiThe provided data is organized in an orderly manner to generate similar forms of program reports. It can be instantly browsed on the TV, which greatly facilitates users' use. This is the guide to Electronic programs.EPG.

SiNo defined9Tables

1, Business Group Association Table (Bat): It provides information about the business group, the name of the business group, and the list of businesses in each business group.

2, Business description table (SDT): It contains the data describing the business in the system, such as the business name, start time, and duration.

3Event info table (EIT): It contains data related to events or programs,EITYesEPG.

4, Running status table (RST): It gives the event status (run/Non-running), the running status table updates this information, allowing automatic adaptation to switching events.

5, Time and date table (TDT): It provides information related to the current time and date. because the information is updated frequently, you need to use a separate table.

6, Time Offset Table (TOT): It provides information related to the current time, date, and Local Time Offset. because the information is updated frequently, you need to use a separate table.

7, Fill table (St): It is used to invalidate an existing segment, for example, at the boundary of a transmission system.

8, Select the information table (Sit): It is only used in a code stream segment. For example, it records a piece of code stream. It contains the location that describes the Business Information segment of the code stream segment.

9, Interrupted information table (Dit): It is only used for bitstream segments. For example, if a recorded bitstream is used, it is inserted into the interrupted service information of the bitstream segment.

It is worth mentioning that,NITInMPEG-2Standards are not specified,SiRules.

these tables are transmitted as data segments in the Transfer Stream, different information tables are transmitted by assigning different PID to distinguish ( for example, table 1 shown ) . With the same PID different information tables are distinguished by the table identifier table id , find these specific PID at the receiving end. TS contains two identifiers: A package identifier and a table identifier. For example, SDT Each table describes the business in a specific TS , these services may be part of the table's TS , it may also be part of other TS . These SDT PID they are all the same. In this case, we can distinguish them using different table identifiers, to identify the business described in that table, the TS .

Table1

Table	PIDValue
Pat	Zero x 0000
Cat	Zero X 0001
PMT	Zero X 0002
NIT	Zero X 0010
SDT,Bat	Zero X 0011
EIT	Zero X 0012
TDT,TOT	Zero X 0014

 

SiIn actual use, each table in does not need to be transferred.NIT,SDT,EIT,TDTIs required, and other tables are selected as needed.

Iii. Guide to electronic programs (EPG)

in DVB system, EPG allows you to conveniently, quickly, and intuitively find the expected program. According to the digital television broadcasting business specifications, you can view EPG requirements, EPG basic functions such as program list and current program playback should be provided, it also provides additional program information, program classification, program reservation, and parental hierarchical control. EPG can use Si , that is, Si Yes EPG prerequisite of the function. In Si , the most important thing is nit , EIT and SDT , use this 3 data in tables can constitute different functions EPG .

NITAs mentioned above,SDTThe role is to provide a description of each business so that users can easily understand the content of each business. For eachTSEach hasSDTCorresponds.EITIt is actually a program, and each program has an independentEIT.

EPGThere are two parts: one is the frontendEPGEditor; second, the control software corresponding to the client receiver. The two parts correspond one to one. The relevant parts of each receiver must be customized according to the data structure defined by the front end, to receive the Business Information sent from the front-end.

SiGenerally, it is synthesized in a multiplex.TSInsert,3Insert method.

1,Insert the table data into the program code stream by means of the application software interface provided by the multiplexing manufacturer.

2,ByMPEG-2Standard packaging, output through the stream broadcasting card, and then send it to the asynchronous serial port of the multier to reuse the program code stream.

3,You can use the interface provided by the conditional receiving spoiler to insert data tables to the spoiler through the LAN.Si.

Iv. Receiver andEPG

DVBA receiver, also known as a set-top box, is a receiverDVBClient devices. When a receiver is opened, there is usually a boot screen, which is actually a menu selection page stored in the set-top box. It is a user operation interface generated by the control software called the loader, you can select an instance through the remote control. The interface developed by each cable TV operator is different, but the function is the same. Its main content is that the operator provides the classification and system settings of the business (Program) and some auxiliary functions. These contents constitute the top menu of the page, and the next menu is usually composedSiGeneratedEPG.

In the main menu, the system is set to enable the receiver to receive messages quickly and accurately.DVBThe program has three basic operations: information detection, program search, and software download.

1, Information Detection: It mainly displays the currentDVBThe system's clock speed and related parameters, such as the clock speed, bit rate, modulation method, bit rate, and equal power signal, are provided for maintenance personnel to check.

Here, the so-called frequency refersSiThe modulation frequency of the code stream.

2Program search: When searching programs, the receiver first searches for the clock speed and finds outSiInformation, and then generateEPG, AlsoEPGGenerate a program list. The program list includes the program name, program description, and program broadcast time. The program list is used as the next menu, and each lower menu item points to the corresponding programTSStream to enable users to conveniently and quickly watch the desired program.

There are two methods for program search: manual search and automatic search. You can manually enter the frequency orDVBAll in the systemTSThe modulation frequency of the stream to guide the receiver to receive the message. The automatic method is that the software sets the relevant receiving parameters and the software guides the receiver to receive the message.

3Software Download: As mentioned earlier, the receiver loader must be customized according to the data structure defined by the front-end. When the front-end needs to change the broadcast program (such as increasing or decreasing the broadcast of the program, adjust the category of broadcast programs) or change the frequency, the receiver loader should also be changed accordingly. Therefore, when the frontend changes to a program, the carrier must simultaneously change the receiver loader and send software update information to all receivers. After the user receives the information, you can use the software download function to update the receiver loader.

To sum up, constituteDVBThe most basic business information of the system should includePSIAndSiBusiness information.EPGBySiGenerate,DVBReceiver dependentEPGTo receive and select to watchDVBProgram.