New Year's initial teaching you how to choose a network video server

In the field of video surveillance, digitalization, networking, and intelligence have become a development trend, and digital video surveillance systems have gradually entered the stage of large-scale commercial applications. Compared with the traditional first-generation analog video surveillance system, the digital video surveillance system has experienced two development stages so far: in the late 1990s, the use of computer multimedia technology to realize the digital monitoring of video images, called the second-generation quasi-digital Local video surveillance system, the typical product is digital hard disk recorder (DVR); in the early 21st century, relying on the network, with digital video processing technology as the core, comprehensive use of photoelectric sensors, digital image processing, embedded computer systems, data transmission networks , A new type of digital monitoring system such as automatic control, artificial intelligence and other technologies was born. It not only has the second-generation local digital monitoring system's rapid computer processing capability, anti-interference ability of digital information, easy to quickly query and record, clear video images and Stand-alone display of multi-channel images and other advantages, and relying on the network, the real advantage of the broadband network, through the IP network, the monitoring center and the network can reach any monitoring target into a system, which is really adapted to the current video surveillance system Remote, real Time and concentration requirements, this is the third-generation fully digital remote video surveillance system, the typical products are network cameras and network video servers.

Although compared with the traditional analog surveillance system, the quasi-digital local video surveillance system based on the digital hard disk recorder is no less than a leap forward, but due to the limitations of its own technical architecture, the digital hard disk recorder has never been able to solve the Problems such as long delay, inability to monitor multiple channels simultaneously, and centralized monitoring with high integration.

Although the network video server product market will not appear as diverse and uneven as the digital hard disk recorder market, the actual product quality and performance differences are still relatively large. Therefore, customers, including security engineering companies, should consider the specific application environment, which is a network environment, and make a purchase decision by weighing the following product standards, performance indicators, and functional integrity.

1. Whether the product has relevant qualifications

Product qualification does not completely represent the quality and performance of the product, but it is the basic condition for the acceptance of many system integration projects, and it is also the basic condition for whether the product is qualified.

Network video server products are security products. According to relevant national regulations, such products should have the inspection report of the special agency of the Ministry of Public Security and the production license of the province where the place of origin is located (foreign products do not require a production license).

2. Intellectual property protection of the product's background management software

However, all network video server products must have supporting background monitoring and management software. Because there are a large number of OEM products and illegal counterfeit products on the market, customers are overwhelmed. Hardware devices can be counterfeited, and software can be copied. In order to prevent illegal soft copies, the original manufacturers often set traps in the software, and illegal copies make users innocent victims. Therefore, whether the background monitoring and management software supporting the product has intellectual property rights will be one of the important standards for customers to judge the product.

3. Actual bandwidth requirements for transmitting standard real-time moving images

This is one of the important indicators to measure the overall performance of the network video server. High bandwidth means an increase in network usage costs. For end users, this will shake their determination to adopt a digital monitoring model. After all, economics is a problem that any business unit has to consider.

Due to different image states (still, normal activity, high-speed motion), image resolution, and the number of transmitted image frames, the network bandwidth occupied by them varies greatly, so many network video server manufacturers always try to blur this when recommending products One indicator. In this regard, we can set a more uniform image state, that is, for normal moving images, the image resolution reaches 352 * 288, and the frame rate is 25 frames per second, the network bandwidth occupied by the video image all the way. The bandwidth requirement of 250K will be a good indicator in the above image state.

4. Delay of remote video transmission

Although the transmission delay is inevitable for any kind of network video server, the delay value of different network video servers is different. The delay value will directly affect the effect of digital monitoring. Imagine that when the surveillance personnel used the mouse to control the front camera pan-tilt in the monitoring center, they clicked the mouse five times within five seconds, and only after the tenth second saw the pan-tilt after the first click How about controlling the effect? Since the transmission delay is different under different frame rates (the same product, the higher the frame rate, the lower the transmission delay), for the sake of comparison and uniformity, the condition is set to 25 frames per second.

5. Alarm pre-trigger recording function

Various network video servers on the market are quite complete in recording function, including real-time recording, timing recording, alarm recording, etc. Alarm recording can be divided into mobile triggered recording, manual triggered recording, external sensor (such as infrared detector) triggered recording Wait. However, in some cases, such as manually triggering an alarm, it is basically started before the end of the accident, and the video recording can only be the image after the alarm is triggered. For the follow-up of the incident, the recorded information is incomplete. At present, there are a few manufacturers of network video servers that already have an alarm pre-trigger recording function, which can save the image signal from several seconds to tens of seconds before the alarm is triggered. This function has special significance for the user to track and judge the alarm event afterwards.

6. Electronic map function

In large-scale video surveillance systems, due to the large number of monitoring sites and wide distribution, the status information of each monitoring point is complex (such as some points set to alarm linkage recording function, some points set to timing recording function, some points set to full real-time recording function, etc. Etc.), the staff of the monitoring center will face complicated and cumbersome operations during selective monitoring, recording, and function setting. The electronic map function can provide a schematic diagram of the distribution of monitoring points in the whole system. The schematic diagram can visually display the distribution status of the monitoring points and the status information of early warning and alarm linkage of the monitoring points. Users can configure the functions of each monitoring point on the schematic diagram according to their needs. Quickly extract video images of monitoring points.

7. IE monitoring function

Conventional monitoring and management software requires complicated training and inconvenience to achieve functional integrity, and even requires special training and learning to be proficient. The network video server management software should be able to provide a simple WEB version of the monitoring and management software choice suitable for leaders or non-professional monitoring and management personnel. It can provide the functions of monitoring, recording, and controlling single-screen images in the form of IE web pages. Users do not need to install professional The software does not need to remember to input the complex IP address of different network video servers when selecting the monitoring image. It only needs to access the WEB server of the system to download the configuration information control such as the name of the monitoring point set in advance. Features.

8. Image compression algorithm standard

The current mainstream network video server compression algorithm standards are nothing more than MJPEG, MPEG-1, MPEG-4, H. 264 and so on. MPEG-4, H. 264 compression technology has high image compression, small bandwidth for network transmission, and convenient storage.

9. The number of video channels that the monitoring center can monitor and record at the same time

Since the network video monitoring server is mostly used for remote, real-time and centralized monitoring of multiple scattered outlets, the number of video channels that the monitoring center can simultaneously monitor and record is an important indicator for measuring the effect of remote centralized monitoring.

10. Number of frames for image transmission from multiple network video servers

The network video servers currently on the market can support one-way or two-way or four-way video image input. Because the more image channels supported, the higher the product technology and processing performance requirements, so most products are single-channel or "quasi-multi-channel" products. What we call a true multi-channel network video server, capable of supporting digital video images of 25 frames per second per output, is truly "real-time". For "quasi-multi-channel" products, no matter two or four channels, the total number of frames of the digital video image output is 25 frames / second, which means that the multi-channel shared 25 frames / second. There is almost no difference. This can be simply judged from the price point. The price difference between the single-channel and two-channel products of some manufacturers is only a few hundred yuan. Basically, the two-channel products can be judged as "quasi-two-channel products".

11. Can it effectively support multiple users to access the same monitoring front end at the same time?

In a large-scale network video centralized monitoring system based on a network video server, a monitoring center usually has multiple monitoring clients, and there are often situations where multiple front-end monitoring outlets are visited at the same time period and real-time monitoring or recording call requests are issued. When there are N monitoring clients in the monitoring center who need to watch the images of a remote monitoring point at the same time (assuming that the bandwidth of one channel is 250K), the bandwidth of the external network is (N * 250) K in normal mode, which usually leads to data jams. Affect the monitoring effect, so the conventional network video server system can generally only support the simultaneous access requirements of three or four clients. The schematic diagram is as follows:

Schematic diagram of large-scale network video centralized monitoring system based on network video server

The "Xiangshi" network video server background management software of Guangzhou Dete Information Technology Co., Ltd. adopts unique streaming media technology, and a "video streaming media management server" can be set up to provide multi-client access to the monitoring network, which solves the problem of simultaneous access by multiple users. The problem of network congestion that occurs in the same monitoring outlet. Since the monitoring center adopts the streaming media service data forwarding mode, a "video streaming media management server" is set up to access and receive front-end monitoring images, and the "video streaming media management server" also serves as a server for internal LAN monitoring clients. Clients with monitoring requirements send monitoring instructions to the "video streaming media management server" and obtain the required front-end monitoring images through them. The biggest advantage of this structure mode is to save the bandwidth resources of the external network. No matter how many monitoring clients in the monitoring center watch the image of a remote monitoring point, the monitoring point only needs to transmit the image to the "video streaming media management server" Sending a viewing request to the "Video Streaming Media Management Server", the external network bandwidth consumption is always only 250K, the schematic diagram is as follows:

Monitoring center adopts streaming media service data forwarding mode

12. Whether to support remote online intelligent retrieval, playback and transcription of local recording materials

Aiming at the application of remote, real-time and centralized monitoring systems for multiple scattered outlets, due to the current scarcity and paidness of public network bandwidth resources, for economic considerations, most users will use ADSL broadband line transmission. At present, the theoretical value of monthly ADSL line bandwidth provided by the telecommunications department is 512K for upstream bandwidth and 2M for downstream, but the actual upstream bandwidth is often only more than 200K. In order to fully meet the needs of monitoring applications, the actual system mostly adopts the functional mode of "central remote real-time round-trip monitoring, local real-time video recording at the branch, and remote remote video viewing at any time. For the remote viewing application of the local recording materials at the outlets, most of the network video server software cannot provide an effective solution at present. , The central monitoring staff will open and watch after receiving, the operation is tedious and time-consuming.

Guangzhou Dete Information Technology Co., Ltd.'s "Xiangshi" network video server supports remote online intelligent retrieval, playback and transcription of local recording materials. The staff of the monitoring center can enter the recording retrieval conditions on the monitoring host when needed, such as outlets The name, camera number, recording time and other elements can immediately establish a connection with the video host of the remote site, play back the relevant video clips, and if necessary, transcribe the video clips to the hard disk of the central monitoring host.

13. Whether to support automatic connection in dynamic IP network environment

In the network application environment based on ADSL broadband line, the access method provided by the telecommunications company to the user is dynamic IP access, that is, the way that the user dynamically obtains the IP address to access the Internet through the virtual dialing technology: the dialer installed by the local computer When driving ADSLModem to dial-up to access the Internet, the ISP will usually randomly assign a public IP address to the user. This IP address is unique before disconnection. Other users can access the user through this IP address, but once disconnected When connecting, the ISP will randomly assign another IP address to the user. In the use of network video servers to achieve remote video centralized monitoring applications, in the network application environment based on ADSL broadband lines, how to easily realize the real-time access of the monitoring center to the monitoring front end under the condition of dynamic IP addresses is still plagued by many engineering companies. , One of the problems of system integrators and network video server manufacturers. At present, many network video servers cannot provide solutions for dynamic IP access. Once an engineering company or user utilizes the network video server and builds a remote monitoring system through ADSL, it may cause the system to fail to achieve the expected functions.

14. Whether it has ADSL automatic dialing function

Conventional ADSL broadband applications must use a computer connected to ADSLModem to drive dial-up Internet access. However, if the ADSL is only used for remote monitoring access, then a computer is specifically configured for each monitoring front end for a simple ADSL dialing function, which will undoubtedly cause a great waste of user equipment resources. Under the above circumstances, the availability of ADSL automatic dialing function will directly affect the user's investment budget.

The "Xiangshi" network video server of Guangzhou Dete Information Technology Co., Ltd. provides the unique "ADSL automatic dialing function" in the domestic similar products, only need to set the ADSL automatic dialing function in the equipment system configuration options, and enter the corresponding ADSL account and password can realize automatic dial-up Internet access.

15. Is it possible to integrate the monitoring system with other management systems

In some system applications, the video surveillance system is just an application subsystem of the entire large system. If the video surveillance system can be organically integrated with other systems, it will greatly facilitate the user's system operation.

16. Warranty issues

The warranty issue is one of the most concerns of engineering companies. Since the contractor directly faces the end user, the unsatisfactory warranty service will directly affect the contractor's reputation. General manufacturers implement a one-year free warranty on products.