Although the network video server product market is not as diverse as the digital hard disk recorder market, the actual quality and performance differences are still relatively large. Customers can weigh the following product performance indicators before purchasing a network video server.

1. 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.

2. 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 transmitted image frame rate, the network bandwidth occupied by them varies greatly, so many network video server manufacturers always try to blur this when promoting 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. According to our understanding, the bandwidth requirements of quite a few manufacturers including Taiwan and South Korea are between 500-600K, and some even require 800-900K.

3. Delay of remote video transmission

Although the transmission delay is inevitable for any 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 on the monitor. Control effect, what will happen?

Due to the different transmission delays at 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. The "Xiangshi" network video server of Guangzhou Dete Information Technology Co., Ltd. adopts MPEG-4 enhanced encoding technology with a transmission delay of no more than one second, which greatly improves the effect of cloud mirror control and remote real-time monitoring.

4. Image resolution

The resolution of the video image after digital processing will directly affect the clarity of the monitored image. The so-called standard image resolution in the current line refers to 352 * 288 pixels and can be adjusted downward, which can be achieved by ordinary network video servers. However, in some special occasions, such as in an unattended power machine room, monitoring almost static measuring instruments through a network video server (need to see the meter scale value) requires higher definition. Guangzhou Dete Information Technology Co., Ltd.'s "Xiangshi" network video server adopts unique sampling technology, which can achieve the highest image resolution of 704 * 576.

5. Image compression algorithm standard

At present, the compression algorithm standards of mainstream network video servers include MJPEG, MPEG-1 and MPEG-4.

The MJPEG compression technology is derived from the JPEG image compression technology, which is a simple intra-frame JPEG compression, and the image clarity after compression is better. However, due to the technical limitations of this method, large-scale compression is not possible, the data volume is relatively high, 1-2G space per hour of recording, and network transmission consumes a lot of bandwidth resources, which is not suitable for the compression of moving object images, nor large It is suitable for the needs of long-term security video recording in China.

MPEG-1 compression technology uses the compression algorithm of multi-frame prediction of front and back frames, which has great compression flexibility and is the most widely used. This algorithm technology has matured and the data compression rate is higher than MJPEG, but the amount of data is still large. The video recording space is 300-400M per hour. If it is used for long-term real-time video recording by the bank, it takes up a lot of hard disk space, especially the network transmission takes up a large bandwidth, which is not practical for remote transmission of video images.

MPEG-4 compression technology is currently the most advanced compression technology that has entered the practical stage. It uses a very narrow bandwidth to compress and transmit images through frame reconstruction technology in order to obtain the best image quality with minimal data. The characteristics of MPEG-4 make it more suitable for interactive AV services and remote monitoring. The MPEG-4 compression algorithm is used. The image compression is relatively high. The video recording space is 100-200M per hour. The image clarity is high. The network transmission takes up little bandwidth and can pass. Various transmission methods for remote video image transmission.

6. 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.

7. The 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 of one-way and two-way products of some manufacturers only differs by about one thousand yuan, and it can basically be judged that the two-way products are "quasi-two-way products".

8. Alarm pre-trigger recording function

Various network video servers on the market are quite complete in recording functions, including real-time recording, timing recording, alarm recording, etc. Alarm recording can be divided into mobile triggered recording, manual triggered recording, and external sensor (such as infrared detector) triggered recording Wait. However, 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.

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June 27, 2020