In the early development of DVR, due to the controversy and variety of the hundreds of companies, the industry concerned felt quite "dazzled", and after a period of change, the classification of various types was roughly formed. According to the "Analysis of the Optoelectronics Industry Development" report of the Optoelectronics Research Institute of the Taiwan Industrial Technology Research Institute, all DVRs are roughly divided into three categories:

One. Digital STB type

STB refers to Set-top Box (generally translated into: digital satellite receiver, set-top box, TV Internet machine, on-demand video box, etc., because the translation name is different, so here collectively referred to as STB). Digital STB type DVR is a functionally integrated signal receiving platform in nature. It mainly provides digital video recording functions and receives digital broadcast and interactive application signals. It can choose to receive digital wireless terrestrial broadcasting (Digital Terrestrial) and digital cable television broadcasting. (Digital Cable), digital satellite communication (Digital Satellite) and other different types of communication signals.

two. PC-based type

The application platform of PC-based DVR is general PC, laptop and so on. Install one or more image capture cards in the PC, use the software to compress the image and perform the image editing function, the system is relatively unstable.

three. Standalone type

The single-model DVR re-uses the CPU and RAM to develop and design, and uses proprietary software programs, which has higher research and development costs. Using hardware compression, the quality is stable, there will be no crash problems, and the image storage speed, resolution and image quality have been greatly improved. This type of product only provides digital recording and playback functions, and does not add other functions such as broadcast signal reception and Internet access. Since the products used in the field of security monitoring mostly belong to the above categories 2 and 3, this article will only discuss these two types. The dispute between the PC-based type and the stand-alone type system is still inconclusive. Although PC-based DVR currently occupies the majority of the market, it is observed that the two types of products will produce market segmentation separately. Yasuhiko Saito, an overseas manager of Japan ’s Ikegami Corporation, which was invested in the development of DVR in 1995, pointed out: "The DVR market will develop in two different directions. On the one hand, due to RTOS (Real Time Operation System) operating It is expected that there will be great development in reliability, but on the other hand, for DVR products that emphasize networked work, the Windows operating system will become another mainstream because of its simple operation.

DVR technology is still in continuous development, and the key technology is the operating system and image compression technology.

One. operating system

1. Using Windows as the operating interface

For DVRs with a PC as the main architecture, the Windows platform ranks first on the list of various operating systems due to its simple use and universal application. Sung-Ik Chang, President of 3R Group in South Korea, said: "At present, most manufacturers of DVR and related products use Windows-based operating systems; especially in large markets like the United States, users tend to use Windows-based operating systems for future maintenance. DVR products ". Jonathan Kim, Manager of Overseas Marketing Department of Korea Digital Logic Company, also said: "We believe that the Windows operating system is the most suitable for the DVR series products. Because Windows is currently a more general operating system, it has high supportability, no matter where Windows is. Can support most related products. "
In addition, Windows is stronger than other operating systems in terms of software upgrades. Since the IT industry is closely related to the security industry in recent years, while digital technology is advancing in the IT industry, related technology development is bound to affect the security industry. The reason why Windows will be loved by many manufacturers is because it has strong upgradeability. The manufacturer believes that since the DVR system cannot stay at a fixed level for a long time, the upgradeability is bound to become the key point of the system development. If the old cost is considered, once the user has higher requirements for the existing system or the original system exposes some defects, most users are unlikely to buy a brand new system to replace it. Upgrade becomes the primary solution.

Although the supplier believes that the stability of the system depends on the actual operation of the user, however, the instability of the Windows operating system itself still makes the user quite questionable. Some manufacturers have stated that if they only use the monitoring system, the Windows 98 system is quite stable; but if they run other programs on the Windows platform at the same time, the system is unstable and even crashes are inevitable.

2. Using Linux as the operating interface

The fierce competition between Windows and Linux operating platforms in the IT industry has also spread to the security industry. Linux is an operating environment that can be used by multiple people, allowing multiple users to use the resources of the computer host at the same time. Linux provides a complete multi-user (Multiuser), multi-tasking (Multitasking) and multi-process (Multiprocessing) environment, which can be downloaded and used on the network. Because its source code is public, it can be developed and modified at will, so Linux users do not need to worry about the lack of required applications, which accelerates the speed of research and development, and the system itself and most of the applications It is free, allowing developers to save a lot of research and development costs. In addition, Linux, which has lower hardware requirements, can save users more investment in hardware costs, and the overall product cost will be reduced accordingly. With the prevalence of the Internet, more and more people use Linux around the world, and it has attracted countless developers to invest in improving the core, developing application software and hardware peripheral drivers, making Linux functions and integrity more and more The focus of attention.

In addition, Linux is an operating system based on the network environment and has complete network functions. Users can connect to the Internet as a stand-alone computer under Linux, and can also set up a local area network (LAN); it can also set up various servers with Linux to provide Mail, FTP, Web ... various services on the Internet and Intranet. Under this trend, Linux has become the operating system that DVR manufacturers are eager to try. Some vendors even said that Linux is more suitable for DVR than Windows. Hyoksang Kwon, associate manager of the Overseas Marketing Department of Eastern Info-Com in South Korea, said: "Since Windows is relatively unstable and the price is quite high, Linux seems to be the most mainstream operating system with potential for development."

In fact, it is still too early to conclude that "Linux as the operating system of DVR will be better than Windows". According to other manufacturers, Linux still has some problems in compatibility, such as printer support, Internet connection, etc., not as good as Windows. In addition, for users who are accustomed to using Windows applications, they will not be able to adapt to the Linux operating method at first; while Linux can read Windows files, Linux still has the disadvantage that it cannot allow Windows systems to read files. In addition, Linux is the operating system that will rise later, so under the current situation that the maintenance personnel are not very sufficient, many users will also have certain psychological barriers when choosing to use the Linux system.

3. Take RTOS as the operation interface

For single-model or non-PC-based DVR, RTOS (Real Time Operation System) is the best operating system. At present, this type of supplier on the market is mainly South Korea and Japan. Many Korean manufacturers such as 3R, Korea Computer Technologies, Kodicom, Artinix, etc. believe that the single-model DVR has the characteristics of high economic efficiency, high stability, and high compatibility with existing security controllers. Launched a single-model DVR. For Japanese manufacturers, they are committed to the development of single-model DVR mainly based on the consideration of image clarity. At present, the image quality of most PC-based DVRs is not as good as that of single-model DVRs.

However, the biggest challenge currently facing single-model DVRs is networking capabilities. Today, with the popularity of networking work, more and more users are using the network, and South Korean Digital Logic ’s Jonathan Kim said: "When we talk about single-model DVR, we often miss the networked remote control part. But DVR If the system cannot be connected to the network, frankly, it cannot be called a DVR system. " Some Western manufacturers have the same view. For example, the United States, Germany, the United Kingdom and other Nordic countries have regarded network functions as the key to digital CCTV products. Mike Fawcett, Executive General Manager of British Dedicated Micros, gave an example: "British chemical and pharmaceutical plants have adopted network-capable DVR equipment. In addition to saving a lot of manpower costs, they can also monitor the status of staff and production lines anywhere, so they save A lot of costs ". The feature of being networkable allows users to monitor remotely via LAN / WAN, Internet and other networks. This feature has been predicted to become the mainstream of the CCTV market in the future. In order to provide products with networking capabilities, single-model DVR manufacturers are caught in a "price vs. function" dilemma. YH Min, general manager of Korea Computer Technology in South Korea, pointed out: "In order for DVRs to have networking capabilities, we must add certain chips to single-model DVRs. To this end, we must increase the amount of investment and costs, in the case of increasingly fierce price competition. Under the circumstances, the increase in costs is very detrimental to us. "

two. Compression technology

At present, the compression technology adopted by DVR is mainly JPEG, MPEG1, MPEG2. Strictly speaking, these compression technologies may not be able to fully meet the needs of long-term recording.

1. JPEG

The compression ratio of JPEG is 20 ~ 80 times, which is suitable for the compression of static images, and there is no room for resolution. In the past, the JPEG compression technology directly processed the entire screen, so it was necessary to wait until the entire compressed file was transmitted before decompressing it into an image screen. This method caused the transmission of a high-resolution screen to take tens of seconds or even minutes. The new generation of JPEG adopts a gradual technology, first transmitting low-resolution image files, and then supplementing the detailed data to improve the picture quality. Although the time required for this method is the same as the original method, users can find this method better because they can see the screen first.

2. MPEG1 and MPEG2

The compression ratio of MPEG1 and MPEG2 is about 100 times (the general VCD and DVD are about 35 times) when the image movement is not large. According to the specifications of VCD and DVD, the resolution of MPEG1 is 320 × 240 (or Below), MPEG2 is usually 720 × 480. MPEG1 and MPEG2 are partial pictures that transmit different actions one by one.

3. MPEG4

As for the compression factor of 450 times (still images can be up to 800 times), the resolution input can be from 320 × 240 to 1280 × 1024 MPEG4, it is designed for mobile communication devices (such as mobile phones) to transmit audio in real time on the Internet / The latest MPEG standard developed for video signals. Compared with the previous version of MPEG4, the biggest difference is that MPEG4 uses the "layer" method, which can intelligently select the difference of the image, and individually edit the screen under compression, which greatly reduces the capacity of the image file. Speed ​​up audio / video transmission. Some people think that the emergence of MPEG4 is undoubtedly a good news for DVR manufacturers. However, some manufacturers believe that although the MPEG4 specifications have been set, the actual technology applied to DVR is not yet mature. Whether it is implemented by software or hardware at this stage All have to be broken through (details in the article "Technology-Application of MPEG4 Compression Technology in DVR").

Opinions on which compression method is more suitable for DVR products are quite different. Sung-IK Chang of 3R Korea specifically pointed out: "In general, the compression technology uses two methods, one is intraframe and the other is Interframe. Interframe can distinguish the difference of each image and only transmit the different parts of the image H.263 and MPEG are representative of this format. The Intraframe method decomposes an animation into several fixed frames and transmits them one by one. Wavelet and Motion JPEG are representative of this method. Considering the transmission efficiency, Interframe is far superior to Intraframe in performance; moreover, Interframe technology can provide quite good picture quality when the screen change is small. " However, users of security products must consider the issue of image quality. At this point, MPEG is inferior to Wavelet and JPEG. Digital Logic's Jonathan Kim said: "We admit that MPEG4 is superior in video compression, but the MPEG series all have image interference and picture distortion. If a user wants to buy a large storage DVR, he can consider MPEG Compression format; but if users want to have good picture quality, they should consider other compression methods; as for which method is good, it depends on customer needs. " Hyoksang of Eastern Info-com believes: "The image resolution is inversely proportional to the image compression rate, the load of the CPU and other related hardware. Because MPEG4 has a very high compression rate, it leads to unclear images. There is still a lot of room for improvement to meet the standards required by the security industry for images. " Mike Fawcett, CEO of DM, further pointed out: "For still pictures, the transmission speed is the same whether compressed by JPEG or MPEG. However, if the object is in motion, the MPEG format will not respond immediately. Transmission, this is because the transmission speed of the MPEG format is slow, or the scenes under monitoring are prone to interference. " He believes that JPEG compression technology is more suitable for the security industry in terms of image quality and transmission speed. He said: "I think the quality of JPEG is better, more competitive and safer." With the continuous development of DVR technology and the gradual expansion of storage capacity, users will inevitably have higher and higher image quality requirements. David Beanland, chairman of Visionfactory in the UK, said: "Although JPEG and Wavelet format images require a large storage space, this compression technology is still mainstream in the DVR industry. Undoubtedly, the storage capacity of DVR will gradually expand, DVRs with a storage capacity of more than 200GB will appear on the market in the slowest after two or three years. Once the capacity problem is resolved, users will focus on the image quality, and MPEG compression technology will be eliminated ". Beanland also questioned whether the images recorded by MPEG compression technology can be used as reliable court evidence. It is still debatable in the European and American markets. Currently working at Philips, Alan Everid with 14 years of experience believes that Wavelet is the best compression method for DVR products. The main reason is that Wavelet removes the high frequency components of the image and only retains the image signal of a single frame. This feature is especially suitable for occasions where the screen changes frequently, such as multi-screen time-sharing display. However, although Wavelet meets the image requirements of the security industry, readers should be aware that Wavelet is not a format commonly supported by the current IT network, so the use of networking will be limited.