Comparison between DVR and network video server

The application of digital hard disk video recorder (DVR) in China is only a few years, but due to its digital advantages, especially in the application of banking systems, a new upsurge has formed in the domestic monitoring industry. It brings a revolution in digital applications to analog CCTV surveillance (cctv) systems.

From the perspective of its function, the hard disk recorder has the functions of video switching, arbitrary image division and combination display, image recording, PTZ lens control, alarm linkage control and remote network transmission control. In a sense, a high-performance hard disk recorder It can replace the matrix switcher, image segmentation and processor, video tape recorder, control keyboard and alarm host of the traditional cctv system to realize a highly integrated digital cctv and alarm monitoring system. From the perspective of long-term development, the digital conversion and compression of the image of the hard disk video recorder can also make the image cheaper and simpler and realize the digital network transmission.

dvr currently uses three technologies: pure hardware decompression, software decompression, and hardware-software combined decompression. Hard disk recorders that use the latter two technologies take up computer cpu and memory resources because of software decompression, so they can process and record images. Is limited in its ability to process images in frames per second. For example, the hard disk video recorder decompressed by pure software cannot process more than 200 frames per second. Under some compression algorithms that require high image quality and high compression ratio, such as mpeg4 format, the number of image frames that can be processed is less, which is 100 Frames / second. Therefore, the hard disk video recorder must be decompressed by pure hardware, and save the computer CPU and memory resources as much as possible, and also reduce the uncertain factors of software operation, so the stability and reliability of the system are greatly strengthened. So now it is the mpeg4 hard compression method that dominates the dvr market.

The so-called mpeg4 hard compression format hard disk video recorder uses pure hardware to decompress the audio and video card. The audio and video are collected, encoded and compressed, and the decoding and display are carried out by an integrated chip. The computer's PCI bus structure is used to directly distribute and transmit multiple audio and video streams to the Computer graphics card, ide bus for image display and storage, the system CPU only plays the role of control and distribution, so the processing of audio and video streams takes up the resources of the computer system and has nothing to do with the number of audio and video channels. In fact, the popular dvr is a high configuration The PC is composed of multiple audio and video compression cards and software bundling.

Although dvr is low in price, low in cost, and has a wide range of applications, it has certain advantages in local monitoring; but like cctv, dvr still uses a centralized monitoring method, and there is no such thing as cameras, codecs / decoders, video cables, etc. Improve. In the application of DVRs in the past, the emphasis is on the recording function, which is mainly based on the small number of channels and large-capacity hard disks. When there are many video monitoring points in the monitoring system, multiple machines are used for cascading applications. The control operation is not very convenient, especially in The medium-sized cctv system still uses the traditional video switcher for front-end video distribution and switching, which cannot achieve system integration. Due to multi-machine transmission of the image network transmission, the remote client login needs to switch the user name one by one, change the ip settings, and login is very inconvenient. Compared with remote monitoring in the network, there is no advantage. The quality and speed of the monitoring screen under the local area network are guaranteed, but it is not complimented in the wide area network. In addition to the need to provide it with a dedicated network access point, and only in the case of high network bandwidth, can ensure the normal transmission of a picture, but the image delay is very serious, there is a remote transmission can not deal with The problem is that if the local dvr transfers images through a shared network, only the clients on the same LAN can monitor the images, but they cannot transfer the images to the WAN, because it can never break through the external network ip to access the internal network. ip this fact. Because it is a PC plug-in card, it will be directly affected by the quality of the PC and the amount of heat generated. It has high requirements on the configuration of the PC and is not easy to maintain. Since most applications are 24-hour cycle recording, the corresponding Hard drive life is very short. In terms of system installation, maintenance, upgrade and expansion, the problems faced by users are still not small. Moreover, the stability of the dvr-based Windows operating system is not good, which may lead to a crash, which is a big problem for relatively demanding monitoring sites. Therefore, in some applications, a large-capacity hard disk recorder with higher integration and more video input channels is objectively needed. But in practical applications, this is unrealistic. Therefore, if the above shortcomings are to achieve remote monitoring in the true sense, dvr is still difficult to achieve.

Network video servers are emerging products in the field of surveillance. Because domestic network providers provide higher network bandwidth and more affordable prices, the Internet has rapidly spread in a few years and gradually penetrated into various industries. It also brought a new revolution to the surveillance field, so people can no longer meet the needs of solidified local surveillance, while the demand for remote surveillance is increasing, the network video server has become a new force in surveillance. .

In terms of digital security monitoring, remote video transmission involves multiple technologies such as data collection, data compression, and network transmission. The use of streaming media technology to form a network video transmission, applied to network video surveillance is a huge breakthrough in the current security field.