Basic digital TV business information and coding knowledge

1.1 Overview of digital TV System

Based on different transmission media and different application fields, DVB standards are divided into several systems: Satellite Digital Television Broadcasting System (DVB-S), Cable Digital Television Broadcasting System (DVB-C ), ground open circuit Digital Television Broadcasting System (DVB-T), Microwave Digital Television Broadcasting System (DVB-M), Interactive Digital Television Broadcasting System (DVB-I), digital television Disturbing System (DVB-CA)

1.2 The Multimedia Home Platform (MHP: multitimedia Home Platform) is a standard developed by the DVB alliance. It is a natural upgrade from pure DVB broadcast to interactive TV applications, it has promoted the transition from analog to digital TV services.

Set-top box is composed of hardware, embedded operating system, MHEG-5 engine and Java virtual machine, middleware and applications, and MHP mainly defines the overall structure of the set-top box, transmission protocol, content format, java Virtual Machine and DVB-J APIs, security and layers of detail. For the transmission protocol, DVB already has the corresponding broadcast and Interactive Data Transmission specifications. To ensure interoperability, you only need to select a mandatory protocol stack that can be used.

Key business requirements of MHP: (1) interoperability between different business providers (2) Scalability (3) Update (4) functional separation between applications and data (5) MHP must be independent from the CA system to support standard (7) Internet access enabled for different Ca systems (6)

MHP aims to allow consumers to use the same set-top box to receive digital services provided by different vendors.

1.3 digital TV Program Guide includes two main forms: Electronic Business Guide (ESG) and Electronic Program Guide (EPG. The Electronic Business Guide is simple and flexible. Similar to analog TV, the receiver manufacturer and user determine the level of detail, appearance style, and channel of interest. The Electronic Program Guide describes the program's broadcast time and content, which helps users (or viewers) conveniently and quickly retrieve programs of interest.

2.1mpeg is a series of international standards developed by the Motion Image Expert Group to use digital compression methods to compress motion images. MPEG-1 focuses on high compression rate, with low bandwidth and low decomposition ability, the video rate is roughly 1.5 Mb/s, And the MPEG-2 bit rate is much higher than the MPEG-1, so it has a higher bandwidth and decomposition force, it can encode audio/video programs of broadcast quality. In addition to the "level" (LL, ML, hl1440, HL) defined based on the image definition, the DVB video standard also defines the "Profile" (SP, MP, the concept of SNR class snrp, space class SSP class, advanced class HP), each different "class" can provide compression tools and compression algorithms that constitute the Encoding System

There are three encoding methods for MPEG-2: Intra-frame compression encoding, inter-frame compression encoding, intra-frame and inter-frame compression encoding.

An image produced by intra-frame compression is called an I-frame. An image produced by intra-frame and inter-frame compression is called B-frame and p-frame, and p-frame is a Forward prediction frame, the previous I or P frame was used to encode the prediction. Several B-frames can be inserted between I-frames and p-frames. B-frames are encoded from the nearest adjacent I-frames or p-frames for Bidirectional prediction. When a p-frame is formed, the reference frame storage only requires the storage of one frame of the image. When B frames are formed, the reference frame storage requires the storage of the first and second frames of the image. The image group GOP is composed of three frames with different prediction and generation relationships: I frame, P frame, and B frame, combined with the sequence start code and sequence first-class data to form an image sequence or basic code stream (es), ES is packaged into PES, and PES is combined into a transmission code stream ts according to the fixed length of 188b and various parameters.

2.2. the DVB open standard covers almost every aspect of digital television broadcasting and defines the channel encoding and modulation modes for satellite, terrestrial, and wired transmission media, and extended the reuse part of the system layer of the MPEG-2, and defined the interface with other networks, making the DVB system a multimedia open system integrating video and audio data, considering the compatibility with existing networks and services, it provides a great space for future expansion of various new value-added services. The core of its specifications mainly include: (1) compression coding part (2) multiplexing part (3) Interface part (4) conditional receiving part (5) Interoperability part (6) transmission part

3.1, MPEG-2 ts is not a transfer reuse, but just a business reuse, IN ts, with an appropriate PID for each TS packet label, to indicate the original stream of the net load in the TS package. There can be many original streams containing multiple different programs. The decoder needs to include additional information in ts to determine which original stream belongs to a program, so as to clearly express the relationship between the obtained program and the PID of the original stream of the program. Such information is the special program information. The MPEG-2 ts transfer packet carries two types of information: compressed audio and video clips and associated symbolic tables. The transferred TS packet is identified by the PID. Therefore, a different PID should be assigned to the data of the transferred data source or a special symbolic table. An ordered arrangement of packets with a given PID is considered as a data stream. The symbolic table described here consists of descriptions of the original stream of the program. These tables are transmitted in segments. Therefore, the symbolic table is called the program-specific information table (PSI)

3.2. Pat defines all programs in ts, and Pat's PID is always 0x000. It is the root node of PSI information and is easily found in ts. To find program information, you must start with Pat. Pat is a complete list of all sections in ts. Pat provides program initialization information transmitted in the TS package. Each program has an entry with the program number and corresponding PID value in Pat. The program number is zero for nit. In Pat, each program is listed together with the PID value containing all PMT values.

3.3. The program ing table (PMT) provides the ing between program numbers and the original code streams that constitute them. This ing table is a set of definitions of all programs in ts. PMT contains control information related to single-channel program multiplexing. The ts of a single program is composed of multiple PES stream multiplexing with the same time base. Each PES is assigned a unique PID, and the relationship between PES and the assigned PID constitutes a PMT. PMT completely describes the program is composed of PES, their PID is what, in the MPEG-2 transport layer, the transmission of PMT code stream called control bit stream, like other PES, it acts as an independent code stream and is transferred in the Net Load of the TS package. It is assigned a unique PID.

3.4. The Conditional Access Table (CAT) provides connections between one or more ca Systems and Their authorization management information: Any special parameters related to the stream and the CA system, each CA system corresponds to a ca_pid.