Development of Audio and Video Technology - Digital TV

    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, and the cost of entering the industry is not very high; it is complicated because it is indeed a very complicated and tedious work to make the set-top box stable, reliable and powerful. Especially in terms of software systems, due to the limitations of STB performance and the real-time nature of use, it cannot support a huge operating environment and programs like a PC, and it lacks complete development tools, which is a problem for software developers. Very challenging job.

The hardware structure
    of the set-top box From the perspective of the composition of the digital TV set-top box, it mainly includes two parts: hardware and software. From a structural point of view, a set-top box is generally composed of a main chip, a memory, a tuner and demodulator, a return channel, a CA (Conditional Access) interface, an external storage controller, and video and audio output.

The function of the tuner and
    demodulator part is to demodulate the transmitted modulated digital signal into a transport stream. The difference of the tuner and demodulator constitutes different digital set-top boxes, such as satellite set-top boxes for QPSK demodulation ( DVB-S), digital set-top box for cable (DVB-C) for QAM demodulation, and digital set-top box for terrestrial transmission (DVB-T) for OFDM demodulation. Thomson, Sharp, etc. are the most popular tuner and demodulator manufacturers in the market. Although some domestic manufacturers produce tuner and demodulators, their market share is very small.

main chip
    With the development of chip technology, more and more manufacturers integrate the functions of set-top boxes into one main chip. For example, most manufacturers now integrate CPU, decoder, demultiplexer, graphics processor and video and audio The processor is integrated in the chip, and even some chip manufacturers represented by Philips integrate the tuner and demodulator in the chip to form an integrated chip solution, which effectively reduces the cost of the device and improves the reliability. In the main chip, firstly, the received transport stream is demultiplexed according to the flag information transmitted by the transport stream, and then the program stream is descrambled according to the descrambling information transmitted by the CA smart card, and the descrambled TS stream is sent to The video and audio decoders decode them respectively, and restore them to AV signals for output. At the same time, various system data tables multiplexed in the TS stream are also separated and sent to the set-top box processor for output respectively.
    In addition, because the CPU and graphics manager are integrated in the main chip, the set-top box can complete more functions. It can run various software to complete many tasks, such as stock receiving, web browsing, etc., and can also realize 2D through the graphics manager. Even 3D graphics processing provides users with a more beautiful interface and realizes various high-quality applications such as interactive games. Since the CPU is the core of the main chip, the performance of the CPU usually determines the performance of the main chip. The performance of the CPU is generally determined by the main frequency. The higher the main frequency, the higher the performance of the CPU. The current fastest CPU frequency has exceeded 400MIPS, and even the most popular and most basic set-top boxes on the market have a frequency of more than 50MIPS. The CPU speed has a certain relationship with the business system running on it. If you need to run an HTML browser in an STB, 100MIPS may be the minimum requirement for the CPU. Of course, this also requires the cooperation of memory.

RAM
    In some respects, a set-top box has many similarities with a PC, and can even be said to be a simplified PC. The most similar thing between the two is the memory. For set-top boxes, memory is mainly divided into Flash memory and SDRAM memory. Flash is used to store the system software, driver software, application programs and some user information of the set-top box. The content can be retained when the system is powered off. At the same time, Flash can update the software on the set-top box in an online manner, so as to achieve the goal of setting the software of the set-top box. purpose of the upgrade. SDRAM is mainly used to store application data. Many functions of the set-top box require memory to achieve, such as graphics processing, video and audio decoding and demultiplexing, etc. The size and configuration of memory are also different for different application requirements. Although the configuration of large-capacity Flash and SDRAM can reserve enough memory space for future business systems, the memory is not the factor that determines whether the software can run. It needs to work with the CPU. Unrealistic high configuration will only cause Waste of resources without contributing to the improvement of STB performance.

External storage devices
    External storage devices generally refer to external hard disks, and large-capacity hard disks can be used to store program streams to meet the individual needs of users. Whether an external hard disk can be installed in an STB is generally determined by the main chip. Only when the processing power of the CPU reaches a certain level can it be possible to support the read and write of the hard disk, and the read and write of the hard disk also requires more memory space.

The smart card interface
    reads the data in the CA smart card through the card reader for descrambling of digital TV programs, especially in today's development of pay TV, it is an essential part of most STBs. In addition to the standard card reader, the common interface CI (CommonInterface) is also used in some STBs to complete the reading of the CA smart card. CI is a standard interface defined by the DVB organization as a set-top box and a separate hardware module. This technology application originated from PCMCIA enables mass production of set-top boxes and brings changes to set-top boxes, and has broad application prospects.

Backhaul communication interface
    With the expansion of set-top box applications, the user's demand for set-top boxes has not only stayed on simply watching video and audio programs, but interactive requirements make set-top boxes embedded with return devices, which can include network adapters, modems, etc. The communication interface is used to satisfy the user to send information back to the front end.

The development of other equipment interface
    technologies has increased the physical interface of the set-top box, such as RS232 interface, infrared remote control interface, wireless keyboard interface, Wi-Fi interface, etc., so that STB can communicate with cameras, DVD, PDA and many other devices. connect.

Software system of the
    set-top box As a client system, the set-top box needs to be equipped with different software systems in addition to having a good hardware platform so that it can complete various tasks. The software in the set-top box can be divided into three main layers: application layer, intermediate interpretation layer and driver layer, each layer contains many programs or interfaces.

Driver Layer
    The driver layer includes the set-top box hardware driver and API interface, which is mainly used to complete the operation of the hardware device.

Intermediate Interpretation Layer
    The intermediate interpretation layer translates the application program instructions of the STB into instructions that the CPU can recognize, so as to mobilize the hardware device to complete the corresponding operation through the driver layer. This layer includes embedded operating system, middleware, CA resident software, etc. Although the use of middleware can bring great benefits to the design and application of STB software, the high cost of use, the increase in hardware requirements and the immaturity of technology make middleware seldom used in China. At present, many software designers use software that directly calls the driver layer to write application programs. Although this can meet temporary needs, with the increase of application requirements, it is a good solution to use middleware in STB.

application layer
    The application layer can be divided into two parts: resident application and downloadable application. Different STB software design concepts make these two parts contain different applications. Reasonable planning of the composition of these two parts will help improve STB’s performance. reliability and response time. At present, there are few applications in domestic set-top boxes, mainly EPG, data broadcasting, stocks, simple download games, etc., and the charm of digital TV is not in watching TV, but in this kind of business application based on digital TV platform, these Applications will improve some of people's daily routines. With the construction of two-way networks and the popularization of interactive applications, there will be more and more interactive application software, which will also bring unpredictable value-added income to operators.

Classification and application
    of STB Different operators and different set-top box manufacturers divide STB into basic, enhanced, and interactive types according to different application habits. Operators have different levels of understanding and application of digital TV. There are also different divisions of STB. different. Most operators define the basic type as only supporting video and audio services and receiving EPG information, without supporting data browsing and other applications, and put these applications in the so-called enhanced type; define the STB with bidirectional function as the interactive type . In fact, it is difficult to distinguish between the basic type and the interactive type in terms of functions. Different business purposes will have different divisions. The so-called basic type and enhanced type often use the same hardware platform, and the difference is only the software. Although some manufacturers claim that their STB is interactive or can carry out interactive services, due to network reasons, there is no mature interactive application in China, and the current so-called interactive applications are basically still local. on an interactive basis.
    The selected chips are different, the hardware platform is different, and other equipment and interfaces are also different, which constitutes a variety of STBs. For example, adding a modem or a network card to the STB constitutes a set-top box with bidirectional function; adding a hard disk constitutes a Personal Video Recorder (PVR: Personal Video Recorder). Of course, these all require the cooperation of software. Set-top boxes of different applications can also be formed by residing different software on the same hardware platform, and the diverse STBs meet the needs of different levels.

The development trend of STB
    The huge market space and the output value of tens of billions have attracted many businesses to engage in the production of STB. It is estimated that more than 300 domestic enterprises are engaged in the production of STB. By the end of 2004, there were about 80 cable digital users nationwide. There are about 10,000 households, except for the more than 300,000 households that have accumulated in the past, the actual number of new users last year will not exceed 500,000 households. The brutality of market competition has made the entire industry in a state of loss. Although operators are currently promoting digital TV on a large scale, engaging in the overall translation of the entire network, and distributing STB to users for free, and for this purpose have also created models such as Qingdao Model, Foshan Experience, and Hangzhou Model, but all of this has not brought the STB industry. Prosperity did not promote the development of STB technology, but caused a lot of confusion to the digital TV industry. How to adapt to the development of technology and grasp the direction of technology development may not only be a problem that manufacturers need to pay attention to, but also should attract the attention of industry authorities and operators. All parties need to make concerted efforts to create a good digital TV as soon as possible. sustainable space.

Digital TV all-in-one machine
    Most of the set-top boxes currently used in China belong to the basic category. They can receive digital TV programs and provide some applications such as e-government services. With the development of digital TV technology, new TV sets with digital decoding function have been launched and are currently in the stage of large-scale testing before they are put into production. This new type of integrated TV that combines the most basic STB and TV functions will have a significant impact on STB's manufacturing and digital TV operations. Facing the huge production capacity and new technologies of home appliance giants products, most STB producers will be at risk of a reshuffle.
    For operators, the emergence of all-in-one machines has also changed operations. In the past, operators not only had to worry about program transmission, but also put a lot of energy into the user's STB, and even carried a heavy burden. All this may be well resolved because of the emergence of the all-in-one machine. In the next 2 to 3 years, according to the national industrial plan, more than 35% of the TV sets produced in China will be equipped with STB function, which means that more than 1,500 all-in-one TVs will be put on the market every year, and this number will continue to increase in the future. keep climbing.

Machine card separation
    The machine card separation and the all-in-one machine are almost a natural pair. The large-scale manufacturing of TV sets not only improves the reliability of products, but also reduces the cost of production. The basis of large-scale manufacturing is that the products produced are consistent, which is not only reflected in hardware but also in software. Software differences prevent manufacturers from producing set-top boxes on the same scale as TVs. Therefore, to achieve large-scale manufacturing, CA is the first problem to be solved.
    The meaning of the machine-card separation technology is to make the receiving device (machine) of the digital TV independent of the CA smart card and its software (card), and the two are connected through an interface product (large card or CAM card), which is reserved by the TV and STB. Generic interface. Before inserting the CA smart card, the software and hardware of all TVs and STBs are the same, and the smart card must first be inserted into a suitable CAM card before it can be inserted into the TV or set-top box to decode the corresponding program. Although on the surface, the use of the CAM card increases the user's access cost, but because of the shackles of the CA, the operator and the manufacturer have brought a reduction in the use and manufacturing costs, and ultimately the user's access cost. decrease. Many advantages make machine-card separation a trend of industrial development. The United States has made machine-card separation a standard for digital TVs, and has defined a mandatory timetable for this. For a big TV producer like China, the separation of machine and card will also become the trend and standard of China's industrial development. As products are put on the market in batches, the popularity of digital TV sets will help drive the development of digital TV users.

Although the interactive STB
    may replace the popular STB, in the development of digital TV, due to the continuous expansion of the business, the software of the STB will also be continuously improved, especially in the interactive field, with the improvement and application of the middleware, the STB It becomes a low-cost hardware platform, which can realize a variety of applications by replacing different software. For operators, interactive applications have huge commercial interests and are the most important source of profit in the future, and the use of interactive STBs can help achieve this goal. Interactive STB also represents the highest level of STB technology development, and has a very huge development space.
    You can store your favorite programs by adding a storage device to the STB. This STB is a PVR. Although PVRSTB has not yet formed a certain market in China, the strong growth in sales of several million units abroad indicates that the domestic market will be huge in the future. As time goes on, this demand will become larger and larger.

Double-decoding or multi-decoding STB
    is a problem for domestic operators, especially in the process of overall translation, how to solve the problem of how to solve the problem of users watching digital TV programs on more than two TV sets, although it can be forced to Sexual administrative behavior achieves one machine and one card, and increases the viewing fee, but it cannot make users understand this operation mode, which also makes the promotion of digital TV face great resistance. Double decoding STB is to use double decoding chips in one STB or embed more than two decoding circuits in one chip, and match with two demodulators, so that one STB can output two different programs, and the cost of STB is only increased by 30% to 50%. The emergence of this new product is undoubtedly a boon for users who own more than two TV sets. Of course, for operators who hope that users can purchase more than two sets of STBs and pay more than two sets of program fees, this Not all good news.

The rapid development of DVB and IP into one
    IP technology has brought a huge threat to digital TV, but in the short term, the two can only coexist and cannot be replaced due to the network cost. Although there are so-called STBs with IP functions in the domestic market, these set-top boxes only integrate network cards or bring backhaul channels. Since they cannot satisfy services such as streaming media, they are not completely a combination of DVB and IP. STB. With the introduction and improvement of chips with MPEG-II and MPEG-IV dual decoding functions, such STBs have been put on the market abroad, which can adapt to different network environments and have broad development prospects. In addition, the development and integration of this technology may bring some unexpected changes to people. Perhaps in the near future, with the development of network technology, a terminal product integrating DVB and IP will become an integral part of the family. It connects the display devices, computers and even other intelligent devices of the family to meet the needs of family informatization.

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