Security surveillance video transmission and wall technology

When the economic level develops to a certain height, people’s material requirements will inevitably increase, and people will pay more attention to the safety of their own living environment. As a result, video surveillance gradually integrates into our daily lives when we look at almost When you surrounded the various video surveillance devices, have you ever been concerned about: how do so many video images are transmitted to the monitoring room or security center? How is it displayed? As we all know, video surveillance is mainly used in the security industry, then let us briefly talk about today's security video transmission and wall technology.

Today's security video transmission

1, analog SD transmission

The analog-standard-definition transmission analog signal is transmitted through the coaxial cable for baseband transmission. When it is transmitted over long distances, the transmission quality will be significantly attenuated. In particular, the attenuation of color signals is even more severe. Therefore, analog signals often have signals added during long-distance transmission. The compensator compensates, in particular, the high-frequency part of the analog SD signal.

2, HD analog transmission

For high-definition simulation, the products that are currently outstanding in the market are the HDCVI of UOB Co., Ltd. and HDTVI of Hikvision. Let's take a look at these two products together.

In November 2012, Dahua Technology Co., Ltd. announced the HDCVI, an analog HD transmission interface technology with independent intellectual property rights. HDCVI technology is based on the existing high-definition video transmission method of the SYV75-3 or SYV75-5 coaxial cable, enabling reliable transmission of ultra-long-distance high-definition video signals on low-cost and low-quality coaxial cables. Compared with HD-SDI subsystem's high requirements for transmission media in practical applications, HDCVI can adapt to longer distances, low-cost transmission media and complex deployment scenarios. It is a low cost, long distance, no delay, high High-efficiency, anti-jamming and easy-to-implement megapixel HD video transmission technology.

Then, in June of this year, Hikvision introduced a new generation of coaxial high-definition HDTVI technology that is dedicated to improving the performance of all aspects of coaxial high-definition, so that high-definition clearer, adaptive device access, the system more intelligent. HDTVI is the abbreviation of High Definition Transport Video Interface, which is the HD video interface. HDTVI technology enables reliable transmission of ultra-high-distance high-definition video signals over existing analog transmission lines. The core of the technology is the HDTVI chip. The front-end camera and the back-end encoder are added with a transmit chip and a receive chip respectively to increase the data transmission distance. Through Hikvision's advanced image processing technology and back-end coding technology, the picture quality is further improved. It avoids the chroma crosstalk phenomenon of the CVBS inherent in the analog system and completely separates the luminance and chrominance signals. HDTVI gave full play to Hikvision's advantages in graphics, coding, and other aspects. It continued the stability of the analog system and inherited the three major characteristics of coaxial high-definition “simple, real-time, and ultra-distance”. HD is simpler and monitoring is more real-time. Transmission more distant.

3, digital transmission

Li Wei, technical director of Zhongwei Electronics, told us that digital transmission is divided into two categories, one is uncompressed digital transmission and the other is compressed digital transmission.

Uncompressed digital transmission

SDI is a serial digital interface, which is digital non-compression technology and comes from the field of broadcasting and television. After the video is converted by analog to digital, there are 2 ways to go, compressed or uncompressed. IP monitoring requires compression. The advantage is that it saves a lot of bandwidth. It is possible for video to be transmitted over IP networks, and it also constrains the storage capacity of video data at the cost of degraded video quality, delays in manipulation, and hidden dangers of open architecture. . Non-compression is the so-called digital non-compression technology, and its standards are many, such as common HDMI, DVI and SDI.

Currently SDI can be divided into three standards according to video resolution and frame rate: SD-SDI is standard definition SDI, mainly for SD resolution, 25 frames per second or 30 frames (PAL and NTSC, respectively), after the conversion of modulus The video bandwidth is approximately 250Mbps (or 360Mbps for 16:9); HD-SDI is high-definition SDI. This standard is mainly for 1080P resolution, frame rate of 25 or 30, and the amount of data after analog-to-digital conversion. It is 1.485Gbps; 3G-SDI is HD high frame rate SDI, the resolution is still 1080P, but the frame rate is increased to 50 or 60, and the amount of data after analog-to-digital conversion is roughly 2.9Gbps.

With the development of high-definition technology, 4K technology has gradually entered people's attention. 4K refers to a resolution of 3840×2160 and an aspect ratio of 16:9. Under this standard, CMOS progressive scan can reach 2160P. With 4K HD IP Camera, the picture quality is more than 2 million pixels, vertical resolution is higher, the picture detail level is more accurate, the display is clearer, cleaner, and more immersive, which can effectively solve the problem. Need for high-definition picture quality and complex lighting monitoring requirements. Afterwards, higher-definition technologies such as 8K and 16K will also appear and be used in the market. By then, video will have a qualitative increase in resolution.

Compressed digital transmission

One of the key technologies of video servers is digital video compression technology. In the current market of network cameras and video servers in China, a variety of compression technologies are available, which can be divided into M-JPEG, MPEG-4, and H. 264 and so on.

M-JEPG uses the intra-frame compression method. The image is clear and stable. It is suitable for video editing and can flexibly set the video resolution and the number of compressed frames for each channel. In addition, its compressed format can read a single screen, so it can be arbitrarily spliced, especially for security purposes. MPEG-4 focuses on solving the problem of transmission of audio and video over low bandwidth. On the bandwidth of 164KHZ, it can transmit 5-7 frames per second on average. Network products using MPEG-4 compression technology can use networks with lower bandwidth. Such as PSTN, ISDN, ADSL, etc., greatly save network costs. In addition, the highest resolution of MPEG-4 can reach 720×576, which is close to the effect of DVD picture. The mode based on image compression determines that it can ensure good definition for moving objects. Its advantages make it one of the important trends in the development of current network product manufacturers. H. The 264 standard has brought moving image compression technology to a higher stage, providing high-quality image transmission at lower bandwidth is a bright spot for its application, H. 264 has more than MPEG and H. 263++ Better PSNR performance.

Li Peng, chief technology officer of Zhongwei Electronics Co., Ltd. believes that the SVAC standard jointly developed by China Microelectronics and the Ministry of Public Security is similar to H. 264, but with independent intellectual property rights, based on its improvement and optimization algorithm than H. 264 More efficient advantages, some provinces have been slowly promoting the technology, but the technology's core technology is only in the hands of Vimicro, but also need to continue to observe the level of research and development and national policies. In general, H. 264 is still relatively successful in domestic use.

4, mixed transmission technology

The use of modular mixed transmission equipment can directly expand and upgrade the original analog monitoring system. Add network digital camera near the original point, just install the camera and power supply, the video (digital) signal of the camera is directly connected to the original coaxial line through the analog/digital transmitter, and then access to the monitoring center. The device separates the D/A signals and inputs them to their respective devices. It simplifies the steps of system construction and saves the cost of secondary wiring construction. It also enables seamless upgrades of analog systems to digital network systems. And Sony's analog mixed transmission is the leader of this technology.

5, optical fiber transmission

Optical fiber transmission transmits video and control signals into optical signals for transmission in optical fibers. It has long transmission distance, low attenuation, and good anti-interference performance. Compared with other transmission methods, it has better image quality and is more suitable for long distances. Transmission is the best solution to solve tens or even hundreds of kilometers of television monitoring transmission. The fiber-optic transmission mentioned here is divided into two types: optical transmission and direct EPON transmission. The development of video optical transceivers in China is accompanied by the development of monitoring. Video optical transceivers are devices that convert one to multiple analog video signals into various optical signals and transmit them through optical fiber media. They are also divided into analog optical transceivers and digital optical transceivers. . The Ethernet Passive Optical Network (EPON) is a new type of optical fiber access network technology. It is the emerging broadband wireless fiber access technology covering the last mile in the world today. It uses a point-to-multipoint structure. Passive optical fiber transmission provides multiple services over Ethernet. It uses the PON technology at the physical layer, uses the Ethernet protocol at the link layer, and implements Ethernet access using the PON topology. Therefore, it combines the advantages of PON technology and Ethernet technology. Passive devices such as optical splitters are used in the middle, and the optical fibers are connected to ONUs to save more fiber optic cable resources, share bandwidth resources, save investment in equipment room, have high equipment safety, build network speed, and comprehensively construct networks. Low cost and other advantages.

The current video surveillance has higher definition than before, and the scale of the point is larger than before. The direct problem that such monitoring brings to the transmission is that the amount of data that needs to be transmitted is multiplied by a geometric level, and to solve these problems. The best and most reliable way to transmit large amounts of data is to use optical fiber. With the further civilianization of optical fiber prices, the current application of optical fiber can be said to be "an old Wang Xietang before Yan, flying into the homes of ordinary people."

Display transmission

The ultimate goal of video transmission must be displayed in front of people in the form of pictures, then you need to display on the video wall. Analog-standard definition is to output the analog video signal to the monitor through the decoder card or decoder's BNC interface to achieve the function of the video wall; Analog HD is connected to the video wall monitor through the DVI interface; while the SDI-level uncompressed digital transmission has special Monitors, generally through the SDI DVR to achieve the purpose of the wall, at the same time it also supports the realization of the wall through the BNC interface; network transmission on the wall is more simple and convenient, it can be directly through the NVR or computer on the wall display, It is said that people are more convenient to use and more convenient to operate.

Security equipment on the wall display

For security-specific equipment, there are generally two types of wall display methods: computer display and local display via a network connection. Among them, the devices that are directly connected to the computer on the wall display directly through the network are the DVRs and NVRs that we often see. There are four common types of local display: HDMI, VGA, DVI, and BNC, where HDMI, VGA, and DVI are high-definition interfaces, while BNC is a standard definition interface.

HDMI (High Definition Multimedia Interface) is a high-definition multimedia interface. It is a digital video/audio interface technology and is a dedicated digital interface suitable for image transmission. It can simultaneously transmit audio and video signals. The maximum data transmission speed is 18 Gbps. At the same time, it is not necessary to perform digital/analog or analog/digital conversion before signal transmission. HDMI can be combined with Wideband Digital Content Protection (HDCP) to prevent unauthorized copying of copyrighted audio and video content. The additional space provided by HDMI can be used in future audio and video formats. HDMI can not only meet the 1080P resolution, but also supports digital audio formats such as DVD Audio, supports eight-channel 96kHz or stereo 192kHz digital audio transmission, can transmit uncompressed audio signals and video signals. HDMI can also be used for set-top boxes, DVD players, personal computers, video games, integrated amplifiers, digital audio and TV dramas. At the same time, it also supports EDID, DDC2B, so devices with HDMI have "plug and play" features, the signal originates from the reality device will automatically "negotiate" automatically select the most appropriate video / audio format.

VGA (Video Graphics Array), a video graphics array, is a video transmission standard using analog signals introduced by IBM in 1987 with PS/2. At the time, it had the advantages of high resolution, fast display speed, and rich colors, etc. The color display field has been widely used. For some embedded VGA display systems, VGA images can be displayed and controlled without using a VGA display card and a computer. The system has the advantages of low cost, simple structure, and flexible application. It can be widely used in advertising and prompting information display in public places such as supermarkets, stations, airports, etc. It can also be applied to the operation information display in the factory floor production process. In multimedia applications and daily life, and after improvements in recent years, VGA maximum output can already reach 1080P HD display.

DVI (Digital Visual Interface) is a digital video interface and uses TMDS (Transition Minimized Differential Signaling) technology to transmit digital signals. TMDS uses advanced encoding algorithms to transfer 8-bit data (each R, G, and B The color signal is encoded by the minimum conversion into 10 bit data (including line and field synchronization information, clock information, data DE, error correction, etc.). After DC balance, differential signals are used to transmit data, which is better than LVDS and TTL. With electromagnetic compatibility, long-distance, high-quality digital signal transmission can be achieved with low-cost dedicated cables.

DVI has two common interfaces. One is the DVI-D interface. This interface can only receive digital signals. The interface has only 3 rows and 8 columns and 24 pins in total. It is not compatible with analog signals, but it can transmit audio and video at the same time. Signal; the other is DVI-I interface, this interface can be compatible with both analog and digital signals, but compatible with analog signal does not mean that the analog signal interface D-Sub interface can be connected to the DVI-I interface, but Must use a conversion connector to use, generally using this interface of the graphics card will have a related adapter. Unlike the DVI-D connector, the DVI-I connector can only transmit video signals.

The BNC (Basic Network Card) interface is a 10Base2 connector, ie a coaxial cable connector. Can cut off the video input signal, make the signal interfere with each other to reduce, and the signal bandwidth is larger than the ordinary 15-frame D-type interface, can achieve better signal response. The network adapter of this interface corresponds to the Ethernet or token network used for the transmission medium using the thin coaxial cable. Currently, the network adapter of this interface type is less common, mainly because the network using the thin coaxial cable as the transmission medium is compared. less. Now it is mostly used in security industry monitors to transmit video signals and cable TV indoor wall interfaces. Only some of the newer products in monitors larger than 17 inches have such an interface. Its video signal input lines are composed of R, G, B and five lines of horizontal scanning and vertical scanning. This connector can separate the input signals of the three primary colors in the video so that they are independent of each other, so as to minimize interference. This improves video input characteristics. Because of this, BNC has always been one of the features of professional-grade displays. However, BNC is currently being replaced by DVI digital video. Of course, BNC will continue to exist for some time before the price and sales volume of DVI equipment can not fully meet market needs.

Camera interface for transmission

In the camera interface mainly used for transmission, analog SD generally has a BNC interface for outputting standard definition signals; analog HD has two BNC interfaces, one for outputting HD signals and the other for outputting standard definition signals. Debugging; SDI has two BNC interfaces and one HDMI interface, one of which is used to debug the BNC interface that outputs analog SD signals, the other is used to output high-definition signals, and the HDMI interface that outputs high-definition digital signals is used for front-end debugging. In addition, the mainstream transmission method of network equipment is RJ-45 interface cable transmission. At the same time, network equipment generally also has a BNC interface outputting analog SD signals for debugging purposes and an HDMI interface for outputting high-definition digital signals.