The hottest network video monitoring system based

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Network video monitoring system based on Embedded Technology

with the rapid development of computer technology and network technology, the world has set off a strong wave of digitization and networking. For the development of public security and security industries, we must experience the stage of analog-to-digital mixing, but the ultimate trend must be full digitization, that is, video is digitalized and networked at the front end, embedded network cameras are used, and networks are used for transmission, Adopt distributed storage system and modular structure to complete the task of video monitoring

I. development history of video monitoring system

video monitoring system has experienced the development process of local analog signal monitoring system, digital monitoring system based on PC card, network digital monitoring system based on embedded technology, etc

1. Local analog signal monitoring system

the local image monitoring system is mainly composed of camera, video matrix, monitor, video recorder, etc. the video from the camera is connected to the monitor by using the analog video cable, the video matrix host is used, and the keyboard is used for switching and control, and the long-time video recorder using tape is used for video recording; Analog optical fiber is used for long-distance image transmission, and optical transceiver is used for video transmission

the traditional analog closed-circuit television monitoring system has many limitations: first, the transmission of wired analog video signal is very sensitive to distance; Secondly, wired analog video monitoring cannot be connected, and can only monitor the site in a point-to-point manner, which makes the wiring work extremely heavy; In addition, the storage of wired analog video signal data will consume a lot of storage media (such as videotape), which is very cumbersome when querying and obtaining evidence

2. Digital monitoring system based on PC card

the remote image monitoring system based on PC is composed of PC card. At the monitoring site, there are several cameras, various detection and alarm probes and data equipment, which are connected to the monitoring terminal through their respective transmission lines. The terminal can be a PC or a special industrial chassis

the terminal of PC based video monitoring system has strong functions and is convenient for field operation. However, the stability is not good, the video front-end (such as CCD and other video signal acquisition, compression, communication) is relatively complex, and the reliability is not high. The PC also needs to be managed by a specially assigned person, especially in the monitoring points where the environment or space is not suitable. This method is not ideal

3. Network digital monitoring system based on Embedded Technology

the monitoring system based on embedded technology does not need to process the PC of analog video signal, but directly converts the analog video signal output by the camera to confirm the accuracy of the experimental machine into IP digital signal through the embedded video encoder. Embedded video encoder has powerful functions such as video coding processing, network communication, automatic control and so on. It directly supports network video transmission and network management, making the monitoring range reach an unprecedented breadth. In addition to the encoder, there are independent hardware modules such as embedded decoder, controller and video server, which can be installed separately, and the equipment of different manufacturers can be interconnected

the advantages of digital video monitoring are that it overcomes the limitations of analog closed-circuit television monitoring: first, digital video can transmit image data on the computer network (local or wide area), which is basically not limited by distance, and the signal is not easy to be disturbed, which can greatly improve the image quality and stability; Secondly, digital video can be connected by computer, and the network bandwidth can be reused without repeated wiring; In addition, digital storage is possible. Compressed video data can be stored in disk array or optical disc, which is very simple and fast

the advantages of the monitoring system based on embedded devices are: because the hardware of this system is an independent device closely bound with the processor and operating system, with specific functions and special design, it is not affected by other software and hardware in the general computer system like the card system, so its performance is more stable, easy to install and maintain, easy to realize the modular design of the system, and easy to manage and maintain

second, monitoring application based on embedded system

in the monitoring application structure based on embedded system, the front end adopts analog camera. Through the process of digitization, compression, packaging, etc., the analog video is transformed into a video stream based on network protocol through the network video encoder, or the integrated network camera is adopted. The networking and digitization are completed at the front end of video monitoring, and the video is circulated through the network for transmission and sent to the video demander. Users of video can use software to decode, display and process on PC, or decode through hardware to output analog video signals to monitor, use keyboard to control, use servers distributed on the network or other types of network storage devices to record video as needed, use pipe system to replace video, and have high requirements for the stability of rotating speed. Since there is no concept of monitoring center, any authorized user can conduct video surveillance and video recording according to their permissions

III. The core technology of the new generation of network video monitoring system

1 Video compression technology

a. still image compression technology: JPEG, M-JPEG, wavelet transform, etc. it uses intra frame processing technology, so the still image is clearer. Wavelet transform is a structure based compression method, which is easy to process and can obtain larger compression than JPEG. But for continuous moving images, files occupy a lot of bandwidth and hard disk

b. moving image compression technology: MPEG-1, MPEG-2, H.263, MPEG-4

MPEG-1 issued in 1993 and MPEG-2 issued in 1994 are the first phase solutions of ISO's moving image expert group (MPEG). In addition to using the intra frame technology, the inter frame technology of Pb frame is used for the first time, which obtains greater compression than the still image compression technology. However, due to the structure based compression technology, the algorithm is fixed and special hardware is used. With the development of software and hardware technology, more content-based algorithms cannot be extended. In addition, its network transmission rate is required to be high, otherwise it needs cache, which can not adapt to the consistent access of various networks with different transmission rates, and its fault tolerance is poor

based on the above reasons, ITU issued H.263 very low bit rate video codec standard in 1998. In addition to the intra technology of JPEG still image compression standard and the inter technology of MPEG-1 and MPEG-2 dynamic image compression standards, the standard also adopts the following four advanced technologies: 1) unlimited use of motion vector mode; 2) Syntax based arithmetic coding mode; 3) Advanced prediction mode; 4) Pb frame mode (prediction diagram, inset). It is a scalable algorithm, which solves the fault tolerance of fault prone networks in view of the changing state of network transmission rate

MPEG formulated the second stage decoding scheme MPEG-4 in 1998. Its open coding system can expand rich content-based coding algorithms at any time, and adopts various transformations including wavelet transform, which can obtain smaller hard disk space and higher definition. In particular, its control of object separation, stronger interactivity and reusability, and content-based hierarchical expansion ensure the best picture quality at the same time under low and high bandwidth

2. Embedded real-time operating system (RTOS)

at present, many monitoring systems use Windows operating system, because Windows provides a large number of graphical interfaces, and there are various external devices and applications, so the development of the system is much easier. However, the windows system is huge and complex, takes up a lot of CPU resources, and the peripheral hardware is more complex. Its stability and reliability are not as good as RTOS system. Because developers master the source code, they can solve hardware conflicts and optimize the system at any time

IV. summary

with the rapid development of computer technology and networking technology, the world has set off a strong wave of digitization and networking. For the development of public security and security industries, we must experience the stage of analog-to-digital mixing, but the ultimate trend must be full digitization, that is, video is digitalized and networked at the front end, embedded networking cameras are used, and networks are used for transmission, Adopt the social distributed storage system of state-owned enterprises and modular structure to complete the task of video monitoring. (end)

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