Guide to digital TV electronic programs (EPG) AND ITS System

 

Due to digital transmission, digital TVs can be combined with multiple services for transmission through one channel. Therefore, digital TV is not a single TV business, but a digital service transmitted through a television transmission channel, including video, audio, images, and data. Global Digital TV has entered a rapid development stage. It is foreseeable that the business related to digital TV will grow substantially in the next few years. The question is, how can users easily find their desired programs and information when digital TV provides users with programs and services that are several times larger than the current number of programs? EPG is obviously an essential tool.

The Electronic Program Guide provides users with an easy-to-use, user-friendly way to quickly access programs. You can also watch one or more channels through this function, even all channels will be played in the near future. At the same time, EPG provides the classification function to help users browse and select various types of programs. Of course, the Electronic Program Guide is also of great significance to business providers.

Digital TV information

1. program description

In digital TVs, all information and signals, including videos, audios, texts, and images, are converted into data after being digitalized. Data should be packed according to the relevant standard (usually MPEG-2) before transmission, forming fixed length transfer (TS) packet, the MPEG-2 TS packet length is 188 bytes, and then quickly transfer to the destination through the network. If there is no boot information for these ts packets with the same length, the receiver decoder cannot find the desired bitstream. Therefore, PSI is defined in the MPEG-2. PSI is used to automatically set and decode the decoder. PSI consists of a program Association Table (PAT), a condition receiving table (CAT), a program ing table (PMT), and a network information table (NIT). Each table is divided into several field mappings (transformations) to ts.

Several PSI tables contain information required to decode and reproduce programs. The main function of PSI is to find programs and code streams to be decompressed. Pat is the root of all tables, and its PID value is 0. In practical applications, when the decoder needs to decode a specific code stream, it must first find pat. Find the program (such as program 1) in Pat, and find the PMT of program 1 Based on the PID of PMT corresponding to program 1 (such as 22. PMT may contain multiple digital bitstreams (including video bitstreams, audio bitstreams, and data bitstreams). Each bitstream also has a PID. If you want to decode the video stream, find the PID of the video stream in the PMT is 54, and then find the pack whose PID is 54 in the Ts, and send all the packets whose PID is 54 to the video decoder. In Pat, program 0 is always reserved for nit.

Here, the PID value is in decimal format. In the related standards, the assigned PID value is in hexadecimal format, which is represented by a value starting with 0 x. For example, decimal values 22 and 54 are 0x16 and 0x36 in hexadecimal notation.

2. Business Information

PSI data provides information that the receiver can automatically set to enable Decoding of different program streams in the reused stream. However, the PSI table cannot provide recognition information about businesses and programs. Therefore, the DVB Organization expands the psi of the MPEG-2 and provides a variety of tables with different types of information, called si. Si is used to describe data such as the transfer system, transfer content, and broadcast data stream schedule. It helps the Integrated Receiver Decoder (IRD) to automatically tune and provide additional information to users, enable ird to automatically set available services.

Si is provided by nine tables, including business group association table (BAT), business description table (SDT), and event information table (EIT). They are divided into several fields and mapped to the TS package for transmission.

In PSI, the content of the network information table (NIT) is dedicated and unspecified. However, in Si table, nit syntax and semantics are defined, and NIT data format is extended, it is designed to provide more information about the physical network.

Unlike Pat, PMT, and CAT in PSI, 9 tables of Si are not forcibly transmitted in actual use. In actual (current) transmission systems, nit, SDT, EIT, and TDT are mandatory. In other transmission systems, nit, SDT, and EIT are optional. Bat, RST, and tot are optional under any circumstances. St, sit, and dit exist only when necessary.

 

Except for the EIT with the time table information, all PSI and SI tables cannot be disturbed to avoid affecting the normal operation of the decoder.

In practical applications, the program broadcasting front end inserts the PSI and SI tables that comply with the standard definition into the TS package to form a digital television broadcasting code stream and transmit it to the user. The receiver Decoder uses the data provided by Si to form the EPG of various functions based on the code streams required for PSI de-multiplexing and decoding. The decoder finds the required bitstream and data based on the package identifier (PID) and Table identifier.

Before inserting ts, the PSI and SI tables are divided into one or several segments. The segment is used to convert PSI and Si into the syntax structure of the TS package, and its length is variable. The length of the EIT segment is limited to 4096 bytes, and that of the rest PSI and SI tables is limited to 1024 bytes. Each segment contains the following elements: Table identifier, table identifier extension, version number, and current/Subsequent indicator.

When the PSI and Si table segments are mapped to the TS package, the corresponding package identifier is provided to indicate the nature of the TS package. The table identifier is used to identify the table where the segment belongs.

The PSI table can only find the code stream to be decoded when you know exactly what the program is and when it is played. It does not provide information about the program and the start time, there is no choice for multiple code streams. With the increasing number of digital TV services, it is inconvenient for users to select Services. If you can organize the information you need in an orderly manner and provide functions similar to program reports and instant browsing on the TV, this will greatly facilitate your use. EPG can play this role.

According to the EPG requirements of the digital television broadcasting business information specification, EPG should provide basic functions such as program list and current program playback, it also provides advanced functions such as additional program information, program classification, program reservation, and parental hierarchical control.

In interactive TV, EPG is more complex and should be able to provide functions such as program content background information, perspective switching, weather forecast, and games.

All these features of EPG can be implemented through the data provided by SI. That is to say, Si is the prerequisite for implementing the EPG function. In the SI table, nit, EIT, and SDT are the most important. Using the data in these three tables, we can construct EPG with different functions.

3. Network Information table

Nit transfer defined in PSI is optional. In Si, nit transfer is mandatory in actual (current) Transfer streams.

Nit indicates the physical network information for transmitting the current business and the characteristics of the network, such as the transmission system (satellite or ground or wired) of the business, and the relevant parameters of the transmission system. Any network is uniquely identified by an independently assigned network Identifier value.

Nit mainly carries network identifiers, network names, transmission system parameters, and other information.

The transfer system has two identifiers: The network identifier and the original network identifier. When NIT is transmitted over the network that generates ts, the network identifier and the original network identifier take the same value. Each service identifier in the original network identifier is unique. When a service included in ts is transferred to another transmission system, the network identifier changes and the original network identifier remains unchanged.

Satellite transmission system parameters include orbital position, orbital East/West Mark, frequency, modulation mode, polarization mode, symbol rate, and forward correction (FEC) inner code.

Wired transmission system parameters include frequency, modulation method, FEC external code, symbol rate, and FEC internal code.

Parameters of the ground transmission system are not defined in China.

The above data provided by NIT is used by the decoder to automatically search for channels. It can also be displayed to provide reference data for users. You can also transmit optional information, such as the network name and service list, in multiple languages.

 

4. Business description table

Each sub-table of the SDT describes the services in a specific TS stream. These services may be part of the actual TS stream or part of other ts streams, which can be distinguished by different table identifiers.

SDT can be divided into several service description segments. Any segment that constitutes the SDT must be transmitted by a TS packet whose PID is 0 × 0011.

SDT provides the business group to which the business belongs, the encryption system used by the business, the link information with other businesses, the quasi-country of the business, the business name and the business provider, and whether the business allows NVOD, multi-screen control, interactive return channel telephone numbers, multilingual service names, and other information.

To make it easier to obtain related services, we generally follow these rules: for actual ts, the transmission of SDT is mandatory, and in the SDT of a specific ts, the SI code stream should at least list all business information in the TS; The SDTS of other TS should list all services of the Ts.

5. event information table

EIT provides information about events contained in each business in chronological order. The types of events are differentiated by table identifiers. For details, see table 2 in digital television broadcasting business information specifications. Any EIT segment is transmitted in a transfer packet with a PID of 0 × 0012

The current/subsequent event information table only contains information about the current and subsequent events in the given business. However, in NVOD, there can be more than two event descriptions.

The information provided by EIT includes the ID number, start time, program length, playback status, and whether to encrypt the event. A detailed description of the event is provided. The time offset of the two events is the same; brief Introduction of multi-language events and program levels.

In all PSI and SI tables, only the EIT schedule can be disturbed.

Composition of Electronic Program Guide

According to the information provided by SI tables such as nit, SDT, and EIT, various EPG types can be formed, allowing users to find the desired information in multiple ways.

In digital TV systems, it is necessary for TV stations and users to add the EPG function, and the information required by EPG is provided by SI.

In fact, various information provided by the SI table is implemented through descriptors. Table 12 in digital television broadcasting business information specification lists the most likely locations of descriptors in the SI table. From this, we can see that the same type of information can appear in multiple SI tables, in addition, it indicates the most likely location of the identifier and is not restricted to using it in other tables. In addition, the information provided by the SI table is not mandatory. This provides great space and flexibility for the development of EPG front-end systems and Si editors. It also shows that EPG is a custom system, its functions are related to what services the program business provider intends to provide to users.

EPG consists of two parts: one is the EPG editor of the broadcasting front end, and the other is the corresponding receiving/display/control software in the digital TV receiver of the user end. The two parts correspond one to one. If a receiver product of a manufacturer needs to enter a transmission network (User Group) that uses an EPG frontend product (data structure encapsulation ), then, the relevant part of the receiver must be transformed according to the data structure defined by the front-end to receive and display the business information sent by the front-end. In the EPG front-end Editor, appropriate descriptors are used to provide relevant information based on the required functions.

Composition of the EPG system

The EPG system consists of the front-end subsystem and the receiver subsystem. The front-end subsystem is mainly responsible for the organization and generation of SI data. Generally, it is done by a dedicated Si Er (SI server, the generated SI data and other program data streams are reused at the system layer and transmitted in the TS stream.

The receiving end subsystem is mainly responsible for receiving and parsing SI data.

 

The Integrated Receiver Decoder (IRD) parses SI data from the received TS stream and establishes a local Si database. The user interacts with the SI database through the EPG interface. To facilitate random access, SI data is repeatedly sent. The retransmission rate is specified in EN 300 468 [1. The receiving end keeps receiving and parsing the SI data from the initiator. When the SI data on the sending end changes, the SI database updates; otherwise, the received SI data is discarded.

 

Application of EPGProgramThe Application Manager is responsible for EPG application management. The upper-layer epg api shields the lower-layer hardware and software entities, when writing EPG applications, you can not consider the specific implementation of the underlying layer, you only need to call the corresponding API function, the underlying DVB-SI API also plays the same role. The lower-layer demultiplexing module receives ts streams, solves the dvb si data streams, and then stores them in the SI information table in the local database through the SI data parsing module, interfaces provided by DVB-SI APIs provide services to the upper layer.

The EPG system implementation solutions at home and abroad are summarized as follows:

(1) local application scheme: This scheme requires program list and detailed information as the form of business information for re-use in the MPEG-2 transmission layer, after the data is transmitted through the channel, the decoder at the receiving end decodes the data and forms a dedicated EPG database in the ram of the receiver. the EPG application retrieves the database and displays the program information that the user cares about based on the instructions entered by the user. The EPG provided by most manufacturers currently adopts this implementation scheme.

(2) interactive implementation scheme: This scheme requires middleware in the software system of the digital TV set-top box (taking the HTML engine as an example). The EPG server at the sending end organizes HTML pages, the set-top box is transmitted to the set-top box through a data broadcast channel. The set-top box displays these pages through the HTML engine, just like browsing web pages in the PC world. The interaction between the user and the EPG is divided into two forms. If there is no backhaul channel, the HTML page usesTa carousel sends messages to achieve local interaction. In the case of a return channel, the set-top box obtains a new page from the network based on user input. This solution is represented by opentv.

Both of the above implementation schemes require that the business information or HTML page be changed with time migration or program modification, and the local application and local interaction scheme also require a certain data retransmission rate, to ensure Random Access to the EPG.

Compared with the above two implementation schemes, the EPG display form of the former is completely determined by the EPG application in the receiver, and the sender only provides necessary information entries, which is easier to implement; the EPG display format of the latter is determined by the page provided by the EPG server, that is, the sender.

Key Technologies of EPG system

The EPG system has the following key technologies: the Organization and generation of SI data at the beginning, the receipt and resolution of SI data at the receiving end, the establishment of the SI database at the receiving end, and the display of the EPG interface. Some of them are implemented by hardware, such as receiving and parsing SI data, and some are implemented by software, such as Si database establishment and EPG interface display. The details are as follows:

1. SI data organization and generation

The organization and generation of the SI data of the initiator is completed by the SI server of the initiator. The Si resolution of the receiver is opposite to this function and is mainly responsible for rebuilding the SI data table. The organization of SI data must comply with the syntax definition in the DVB-SI and the syntax definition of the MPEG-2, while looking at all the business information in the transmission network. The information content should correspond to the information in the PSI and SI tables. It can be described in hierarchical order according to the network-Transport Stream-service-event and embedded with transport stream-Program (service) -layered sequence of element stream.

 

2. Si database creation

SI data must be stored according to a certain data structure, so as to conveniently and quickly retrieve and extract data. In particular, for EPG systems that run on the real-time operating system of the set-top box, real-time actions must be performed on user interactions. The quality of Si database establishment has an important impact on its performance. SI data mainly includes network information, transmission stream information, business (Program) information, and business event information. A large amount of information is transmitted through descriptions, therefore, you can use a tree-linked list to store data and construct a tree structure from the network, transmission stream, business, and event, the description child that transmits different information is represented by the Child class that inherits the same base class.

3. Display Technology of EPG system

When the TV program and EPG application start at the same time, the user may see the overlapping of the Program Screen and EPG interface. The TV screen displayed by the user can be divided into three layers, the graphic layer, video layer, and background layer are arranged in sequence.

The graphic layer here is the OSD (on screen display) layer. The OSD interface display technology refers to overlapping text display on the image, enable the screen to provide more additional information. The video layer is the program currently being watched (decoded activity image); the background layer is the screen image when the TV program is not played and the EPG menu is started. The EPG screen is built on the graphic layer. The EPG screen is composed of multiple EPG graphic elements (such as buttons, text boxes, buttons selected, and component containers. The status transition of the interface is implemented through the message-driven mechanism, and the message is processed in the message response function. The screen image you see is the layer-3 blend image.

The overall idea displayed on the EPG interface is to separate SI data from graphic elements. It includes the following parts: SI data retrieval and extraction, Graphic Element Library required for the EPG interface, status transfer controller, and OSD layer plotting engine, the blend operations on the OSD layer, video layer, background layer, and Layer 3. The SI data retrieval module quickly retrieves the local Si database and provides the data information required for the current input focus on the EPG interface. The OSD layer Graphic Element Library provides the graphic elements required for the interface, the inventory is stored in the ROM of the local set-top box. The status transfer controller receives the input from the user's remote control, displays the desired activity focus, and controls the status transfer direction; the OSD layer image refers to the image after the graphic elements of the EPG interface are merged. The OSD rendering engine determines the correspondingAlgorithmReceives the data provided by each module, draws the OSD layer image, and finally blend operations on the OSD layer, video layer, and background layer.

The advantage of digital TV is not only to provide high-quality video and audio programs, but also to provide business flexibility and diversity after digital processing. The Electronic Program Guide describes the program's broadcast time and brief content, which helps the audience quickly find programs they are interested in. This will greatly help viewers watch TV. We must pay attention to the research of digital TV's electronic program guide system and the preparation of content.