“Overview of Network Video Surveillance System Based on Embedded WEB Technology At present, network-based digital video surveillance system is the mainstream of video surveillance system development. With the advancement of microprocessor technology and computer network technology, embedded WEB-based network The video surveillance system has gradually attracted widespread attention. The main principle is that the embedded video server adopts an embedded real-time operating system and has a built-in embedded WEB server. After the video signal sent from the camera is compressed by the high-efficiency compression chip, it is transmitted through the internal bus to the built-in WEB server.The user can watch the web server directly through the browser on the monitoring terminal
1. Overview of network video surveillance system based on embedded WEB technology At present, network-based digital video surveillance system is the mainstream of video surveillance system development, and with the progress of microprocessor technology and computer network technology, embedded WEB-based digital video surveillance system is the mainstream of video surveillance system development. The network video surveillance system has gradually attracted widespread attention. The main principle is: the embedded video server adopts an embedded real-time operating system, and a built-in embedded WEB server. The bus is sent to the built-in WEB server. On the monitoring terminal, the user can directly view the video image of the camera on the WEB server through the browser, and the authorized user can also control the action of the PTZ lens of the camera. The schematic diagram of the monitoring system described in this paper is shown in Figure 1.
The system consists of cameras, embedded WEB server, transmission network and monitoring terminal. Cameras are used to capture video of the surveillance site. The embedded WEB server is the core of the whole monitoring system. It has two parts: hardware and software. The detailed structure will be introduced separately below. Its main functions include: providing a WEB access page for the monitoring terminal; checking the validity and security of the access of the monitoring terminal; responding to the request of the monitoring terminal, providing the required video image for the monitoring terminal; receiving the control information of the monitoring terminal, through software and hardware conversion Then control the camera. Each server has its own IP address, and the monitoring terminal can access the server through the browser interface. The function of the monitoring terminal is to Display the live video, and send video requests and control signals to the camera to the server as needed.
2. The hardware structure of the embedded WEB server
The hardware structure of the embedded WEB server is shown in Figure 2. It is mainly composed of CPU chip, MPEG-4 audio and video coding chip, Flash chip, SDRAM memory, Ethernet network interface, and large-capacity hard disk. Among them, the CPU adopts PowerPC series embedded communication processor MPC8250 of MOTOROLA Company. The MPEG-4 audio and video encoding chip completes the compression and encoding of the video data transmitted from the camera. According to the network bandwidth, topological structure and the requirements for image quality, this system selects the hierarchical scalable coding scheme based on MPEG-4 standard. The compressed video data can be stored in a large-capacity hard disk or transmitted over an Ethernet network as required. In order to realize the video storage function, a large-capacity hard disk is required.
Figure 2 Hardware structure of embedded WEB server
3. Software system of embedded WEB server
The software design and realization of the embedded WEB server is one of the keys to the realization of the system, including the embedded operating system and application software.
3.1 Embedded operating system
Embedded operating system is an operating system software that supports embedded system applications. The system adopts the embedded LINUX operating system, which is realized on the basis of miniaturizing and real-time cutting the LINUX operating system according to the needs of the system. The advantages of using LINUX are: the source code of its operating system is open and can be customized according to needs; the system kernel is small, so the hardware requirements are relatively low; it supports multi-tasking and multi-process, and can provide better real-time performance.
3.2 Application software
The application software structure of the server is shown in Figure 3. It is mainly composed of several important parts such as WEB server, CGI program, embedded database mSQL, video scheduling and transmission module, storage management and scheduling module, and camera control module.
3.2.1 WEB server and CGI program
The WEB server exchanges information with the monitoring terminal browser software through the HTTP protocol, and provides interfaces for other application modules, video data browsing interface and camera control interface. In addition, it also controls the access rights of the monitoring terminal, filters the request and control information of the monitoring terminal, and handles the synchronization and priority issues of the requests and controls of multiple monitoring terminals. This system chooses the Boa WEB server which is suitable for the embedded system. Boa is a single-task HTTP server that supports CGI technology that can realize dynamic WEB technology, with open source code and high performance. At the same time, the server program itself occupies a small space, so it is very suitable for embedded systems. At the same time, the system adopts CGI (Common Gateway Interface) to realize dynamic WEB technology. CGI specifies the interface protocol standard for the WEB server to call other executable programs (CGI programs). The WEB server realizes the interaction with the browser by calling the CGI program, that is, the CGI program accepts the information sent by the browser to the WEB server, processes it, and sends the response result back to the WEB server and the browser. Principle CGI programs can be written in any programming language, but CGI programs written in C language have the characteristics of high execution speed and high security.
Figure 3 Application software structure of embedded WEB server
3.2.2 Embedded database mSQL
In this system, the storage of user information, the user’s login and logout, the storage and query of video equipment parameters, and the storage and query of video files all require an embedded database. Comprehensive consideration, this system uses mSQL (MiniSQL) as the background database of this system. mSQL is an excellent embedded database with a compact architecture and less system resources. It is especially suitable for use in embedded Linux systems. At the same time, mSQL provides special API functions, so that CGI programs written in C language can communicate with the database engine of mSQL.
3.2.3 Video scheduling and transmission module
The video scheduling and transmission module provides the required real-time video information for the monitoring terminal, and is the most important module in the server application software. This module establishes a connection with the monitoring terminal according to the adopted network transmission and control protocol, and monitors the monitoring terminal’s request; at the same time, according to different service types, it adopts the corresponding scheduling strategy to create a video stream, and then groups and packages the video data and sends it to the monitoring terminal. , and perform error processing and congestion control according to the network status information fed back by routers and monitoring terminals.
The transmission of video data generally adopts the UDP network communication protocol, and the IP transmission methods of UDP are three kinds of on-demand, broadcast and multicast. The multicast is that the server only sends a data packet to a specific user group, and each user in the group can This packet is shared, but users outside the group cannot receive it. This system adopts IP multicast mode, and the advantages of using multicast technology are as follows: the server can bear the video data broadcast requirements of a large number of clients; due to the small number of data packets copied and the sending destination address, the data transmitted in the network is greatly reduced. In order to ensure a higher quality of service; reduce the bandwidth occupation of video data stream transmission, reduce the burden on the server.
The network transmission protocol adopted by this system uses the RTP/UDP/IP model. The RTP protocol is a protocol that provides end-to-end real-time media transmission services. It consists of two parts: the real-time transmission protocol RTP and the real-time transmission control protocol RTCP. RTP is used for the transmission of real-time video data, while RTCP is used to monitor the transmission of real-time video data. The RTP/UDP/IP method takes into account the real-time performance and QoS guarantee of video transmission. At the same time, certain congestion control and error control strategies can be adopted for the uncertainty of the transmission network condition.
3.2.4 Storage Management and Scheduling Module
The main function of the storage management module is to store the compressed and encoded video information in a specific area of the disk according to a certain strategy, and store the video file information in the embedded database for retrieval and playback, and respond to video scheduling and The request of the transmission module reads video data from the disk to the memory buffer according to a certain disk scheduling policy and priority order. For storage management, the system adopts the equal-length grouping storage strategy, that is, the video information is divided into several data units according to the time sequence relationship, these data units are called groups, and each group is stored in a fixed-size storage unit.
3.2.5 Camera Control Module
The camera control module mainly realizes the control of the camera. On the monitoring side, the user sends the camera control command to the WEB server through the browser. After the control command is accepted and processed by the WEB server, it is sent to the camera control module through the CGI program, and then converted into the corresponding hardware operation instructions for camera control. , so as to realize the remote control of the camera pan/tilt lens.
4. Monitoring terminal browsing
The system uses a browser at the monitoring end to monitor the monitoring site. The platform that the browser runs is independent of the platform that the embedded WEB server runs, and no third-party software is required to browse the remote video, thus realizing cross-platform. The interface of using this system to browse video on the monitoring terminal is shown in Figure 4.
Realization of video image display of monitoring system based on WEB server
Figure 4 Surveillance end browsing video interface
This paper introduces the design and implementation of a network video surveillance system based on embedded WEB technology. Compared with the traditional network video surveillance system, the main features of this system are: the design of the server is based on embedded WEB technology; it supports dynamic IP, can Directly connected to the Ethernet, it can be plugged and viewed; users can watch only with a browser without using special software; at the same time, the system adopts the advanced MPEG-4 encoding standard, which greatly reduces the amount of data while improving the video quality. . It is believed that with the popularity of network video surveillance, the network video surveillance system based on embedded WEB will have a good development prospect.
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