Development of audio and video technology-Digital TV

Source: Internet
Author: User

In today's digital TV industry chain, digital TV set-top box (STB) is a simple and complex consumer terminal product. It is simple because it is very simple to produce a set-top box, the cost of industry access is not very high; it is complicated because it is a very complicated task to make the set-top box stable, reliable and powerful, especially in software system, because of the limitation of STB performance and the real-time of use, It does not support large operating environments and programs like a PC, and lacks sophisticated development tools, which can be a challenging task for software developers.

The hardware structure of STB

From the structure of digital TV set-top box, it mainly includes two parts: hardware and software. From the structure, the set-top box is generally composed of main chip, memory, tuning demodulator, Return channel, CA (conditionalaccess) interface, external storage controller and AV output.

Tuning Demodulator

The function of the tuning demodulator is to restore the modulated digital signal transmitted over to the transmission stream, the difference of the tuning demodulator constitutes a different digital set-top box, for example, the satellite set-top box (dvb-s) for QPSK demodulation, A wired digital set-top box (dvb-c) for QAM demodulation and a terrestrial transmission digital set-top box (DVB-T) for OFDM demodulation. At present, the market is more popular tuning demodulator manufacturers have Thomson, Sharp, and so on, although some manufacturers in the domestic production of tuning demodulator, but the market share is very small.

Main chip

With the development of chip technology, more and more manufacturers integrate the function of set-top box into a main chip, for example, most manufacturers now integrate CPU, decoder, multiplexer, graphics processor and AV processors in the chip, Even some of the chip manufacturers represented by Philips have integrated the tuner into the chip to form an integrated chip solution that effectively reduces device costs and improves reliability. In the main chip, first, according to the transmission flow of the flag information transmitted to the received transmission stream to be multiplexed, and then according to the CA smart card transmission of the disturbance information to the program stream to be disturbed, the solution of the TS sent to the AV decoder, respectively, to decode it, to restore the audio signal output, at the same time, It also separates all kinds of system data tables which are reused in TS Stream, and gives the set-top box processor output separately.

In addition, due to the integration of the CPU and graphics Manager in the main chip, so that the set-top box can complete more functions, it can run a variety of software to accomplish many tasks, such as stock reception, web browsing, etc., can also be achieved through the Graphics Manager 2D or even 3D graphics processing, to provide users with a more beautiful interface, Achieve a variety of high-definition applications such as interactive games. Since the CPU is the core of the main chip, the performance of the main chip is usually determined by the CPU. CPU performance is generally determined by the frequency, the higher the frequency, the higher the performance of the CPU. At present the fastest CPU frequency has exceeded 400MIPS, even in the current market, the most basic set-top box CPU frequency is also more than 50MIPS. CPU speed is bound to the business system running on it, if you need to run an HTML browser in an STB, 100MIPS may be the minimum CPU requirements, of course, it also requires memory mate.


In some ways, the set-top box has many similarities to the PC, or even a simplified PC, the most similar of which is memory. For set-top boxes, memory is mainly divided into flash memory and SDRAM memory. Flash used to store set-top box system software, driver software, applications and some user information, in the system power down the content can also be retained, and flash can be in the online way to update the software contained on it, to achieve the purpose of set-top box software upgrade. SDRAM is primarily used to store application data. Many functions of the set-top box require memory, such as example processing, AV decoding and multiplexing, and different application requirements, and the size configuration of the memory varies. The large capacity of the flash and SDRAM configuration, although the future business system can reserve enough memory space, but memory is not to determine whether the software can run the factors, it needs to work with the CPU, the impractical high configuration will only cause the waste of resources, and does not help STB performance improvement.

External storage devices

External storage device generally refers to the plug-in hard disk, large-capacity hard disk can be used to store program flow to meet the individual needs of users. A STB can be external hard disk is generally determined by the main chip, only the CPU processing power to a certain extent, it is possible to support the hard disk read and write, and hard disk read and write also need more memory space.

Smart Card Interface

Reading the data from the CA smart card through the card reader is used for the solution of digital TV programs, especially in the development of pay TV today, which is an essential part of most STB. In addition to the standard card reader, common Interface ci (commoninterface) is used in some STB to complete the reading of the CA smart card. CI is a standard interface defined by the DVB organization between a set-top box and a separate hardware module. This kind of technology application originated from PCMCIA, so that set-top box can be mass production, also bring the change to set-top box, have a wide application foreground.

Backhaul Communication Interface

With the expansion of set-top box applications, so that users of the set-top box is not only the need to stay in the simple viewing audio programs, interactive requirements of the set-top box embedded in the backhaul device, these devices can include network adapters, modems and other communication interfaces, to meet the user information back to the front end.

Other device interfaces

The development of new technology makes the physical interface of set-top box increase constantly, such as RS232 interface, infrared remote control Interface, wireless keyboard interface, Wi-Fi interface and so on, so that STB can connect with many devices such as camera, DVD, PDA and so on.

Software system of STB

Set-top box as a client system, in addition to having a good hardware platform needs to be equipped with different software systems to complete a variety of tasks. The software in a set-top box can be divided into three main layers: the application layer, the intermediate interpretation layer and the driving layer, each of which contains many programs or interfaces.

Drive Layer

The driver layer includes the driver and API interface of the STB hardware, which is mainly used to complete the operation of the hardware device.

Intermediate interpretation Layer

The intermediate interpretation layer translates the STB's application instructions into instructions that the CPU can recognize, thereby enabling the drive layer to mobilize the hardware device to perform the corresponding operation. This layer includes embedded operating system, middleware, CA resident software and so on. Although the use of middleware can bring great benefits to the design and application of STB software, the high cost of use, the increase of hardware requirements and technical immaturity make middleware seldom used in China. At present, many software designers use the software to directly call the driver layer to write the application, although it can meet the needs of the moment, but as the application needs increase, in the STB using middleware is a good solution.

Application Layer

The application layer can be divided into the host application and the downloadable application two parts, the different STB Software design concept makes these two parts contain the application also not identical, the reasonable planning these two parts composition will help to improve the STB's reliability and the corresponding time. At present, the application of domestic set-top box is less, mainly to EPG, data broadcast, stock, simple download game, and so on, and the charm of digital TV is not to watch TV, but lies in this business application based on digital TV platform, these applications will improve people's daily life customs. With the construction of two-way network, the popularization of interactive application, based on interactive application software will be more and more, this will also bring unpredictable value-added revenue to operators.

Classification and application of STB

Different operators and different set-top-box vendors according to different application habits to the STB into basic, enhanced, interactive, and so on, operators of digital TV understanding and application of different levels of STB Division also differs. Most operators define the basic type to support only AV services and receive EPG information, do not support data browsing and other applications, and place these applications in so-called enhanced types, and define an STB with bidirectional functionality as an interactive type. In fact, it is difficult to distinguish between what is the basic type and what is interactive, different business purposes will have different division, so-called basic and enhanced is often the same hardware platform, the difference is only software, although there are manufacturers claiming that their STB is interactive or can carry out interactive services, However, due to network reasons, there is no mature interactive application in China, so-called interactive applications are basically still on the basis of local interaction.

Choose the chip different, the hardware platform is different, equipped with other devices and interfaces are also different, this constitutes a variety of STB. For example, by adding a modem or network card to the STB, a set-top box with two-way function is formed, and the hard disk is the personal video recorder (Pvr:personalvideorecorder), which requires the cooperation of the software. In the same hardware platform through the presence of different software can also constitute different applications of set-top boxes, and diversified STB to meet the different levels of demand.

The development trend of STB

Huge market space, tens of billions of of the production value attracted a large number of businesses engaged in STB manufacturing, it is estimated that more than 300 domestic enterprises are engaged in STB production, and up to the end of 2004, the national cable digital users around 800,000, excluding the previous cumulative development of more than 300,000 households, In the last year, no more than 500,000 new users, the brutal market competition makes the whole industry in a state of loss. Although at present the operators in large-scale promotion of digital television, the entire network of the overall translation, to users free STB, for this also created such as the Qingdao model, Foshan experience and Hangzhou model, but this did not bring STB industry prosperity, nor promote STB technology development, On the contrary, the digital television industry caused a lot of confusion. How to adapt to the development of technology, grasp the direction of technological development, may not only be the manufacturers need to pay attention to the issue, perhaps more should be caused by industry authorities and operators concerned, the need for concerted efforts to create a good digital TV space for sustainable development.

Digital TV Integrated Machine

At present, most of the set-top boxes in domestic use belong to the basic category, they can receive digital TV programs, also can provide some applications such as e-government services. With the development of digital TV machine technology, new TV sets with digital decoding function are available, and are now in the large-scale testing stage before putting into production. This new integrated television set, which combines the most basic STB and TV functions, will have a major impact on the operation of STB's manufacturing and digital television, and most STB producers will face the risk of re-shuffling in the face of the huge production capacity and new technology products of the home appliance giants.

For operators, the advent of the integrated machine has also changed the operation. In the past, operators should not only worry about the transmission of the program, but also devote a lot of energy to the STB, and even carry a heavy burden on the back, especially in the process of overall translation, because of the sending STB and bear the huge debt, and all this may be due to the emergence of a machine and get a good solution. In the next 2-3 years, according to the national industry planning, the domestic production of more than 35% of televisions will have STB function, which means that more than 1500 units per year will be put on the market, the number will continue to climb.

Machine Card Separation

Machine card separation and all-in-one machine is almost a natural pair. The large-scale manufacture of televisions not only improves the reliability of products, but also lowers the cost of production, while the basis of mass manufacturing is the consistency of products produced, not only in hardware but also in software. The difference in software makes it impossible for manufacturers to produce set-top boxes as large as televisions. Therefore, the implementation of scale manufacturing, CA is the first problem to solve.

The meaning of the Machine card separation technology is to make the digital TV receiving device (machine) and CA smart card and its software (card) Independent, both through an interface product (kcal or cam card) to connect, TV sets and STB reserved this universal interface. Before inserting the CA smart card, all the TV sets and STB hardware and software are the same, and the smart card first to plug into a suitable cam card in order to plug into the TV or set-top box, to solve the corresponding program. Although the use of the cam card to increase the user's access cost, but due to the separation of the CA's binding to operators and manufacturers have brought the cost of use and manufacturing lower, and ultimately bring the cost of user access to reduce. Many advantages make the machine card separation become a trend of industrial development, the United States has separated the machine card as the standard of digital TV, and to this end defined a mandatory timetable. For such a large television producer in China, the separation of the machine card will also become the trend and standard of Chinese industry development. With the volume of products to market, the popularization of digital TV will help to promote the development of digital television users.

Interactive STB

Although the whole machine may replace the popular STB, but in the development of digital TV, due to the continuous expansion of business, STB Software will continue to improve, especially in the interactive field, with the improvement and application of middleware, STB becomes a low-cost hardware platform, can be replaced by different software to achieve a variety of applications. For operators, interactive applications have huge commercial benefits and are the most important source of profit for the future, and the use of interactive STB can help achieve this goal. The interactive STB also represents the highest level of STB technology development, and has a huge development space.

By adding storage devices to the STB, you can store your favorite programs, the STB being the PVR. Although the current PVRSTB in the domestic has not formed a certain market, but the strong growth of millions of units of foreign sales each year is indicative of the huge domestic future market, with the passage of time, this demand will be more and more large.

Dual decoding or multi-decoding STB

For domestic operators, especially in the process of overall translation, how to solve the user two or more TV sets to watch digital television program is a headache for developers, although the mandatory administrative behavior can reach a machine one card, improve the subscription fee, but can not let users understand this mode of operation, It also makes the popularization of digital TV face great resistance. Dual decoding STB is a STB in a dual decoder chip or embedded in a chip more than two decoding circuit, and with two demodulator, so that a STB output two different programs, and STB cost only increased 30%~50%. The advent of this new product is undoubtedly a boon for those who have more than two televisions, and of course this is not good news for operators who wish to buy more than two sets of STB and pay more than two of the program fees.

DVB and IP Merge

The rapid development of IP technology poses a great threat to digital TV, but in the short term, because of the network cost, the two can only coexist and cannot be replaced. Although the current domestic market has so-called STB with IP capabilities, but these set-top boxes are only integrated with the network card or with a backhaul channel, because they can not meet the streaming media and other services, so it is not entirely a DVB and IP into a single STB. With the introduction and perfection of MPEG-II and Mpeg-iv dual decoding function chip, overseas already have this kind of STB put on the market, it can adapt to different network environment, have broad development foreground. In addition, the development and integration of this technology may bring some unexpected changes, perhaps in the near future, with the development of network technology, a set of DVB and IP in one end product will become a member of the family, it is connected to the home display equipment, computers and even other intelligent equipment, To meet the needs of family information.

Development of audio and video technology-Digital TV

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