HD network cameras represent the future of surveillance cameras. The application of high-speed network transmission technology represented by optical transmission system in China is becoming more and more popular. The ultra-high-speed backbone network spanning a large geographical area and the high-speed network in a local area have become the normal facilities. The real-time transmission of high-definition images of large-scale streams through the network has been It is possible, and there is room for constant downward adjustments. These have opened up a broad space for HD surveillance.
HD network camera is very important
We know that traditional SD monitoring is divided into three types: analog, digital and network. The front end of the analog monitor is the analog camera and the back end is the matrix. The front end of digital surveillance is also an analog camera, and the back end is a DVR. There are two types of front ends for network monitoring. One is an analog camera video encoder, the other is a network camera, and the back end is a platform. That is to say, in the era of standard definition monitoring, the front end has various types such as analog cameras, network cameras, and video encoder analog cameras.
The current high-definition video sensor is mainly CMOS. The CMOS sensor directly outputs the digital video signal. The digital high-definition video signal is directly compressed and encoded by the DSP or ASIC in the camera, and then transmitted in a networked manner, and the HD signal is directly outputted than the camera. It is economical and more efficient.
HD network cameras offer a clearer visual experience while also placing higher demands on network bandwidth. In order to get a large-scale application, in addition to passively expecting network operators to make some adjustments, it is necessary to take some alternatives to alleviate the contradiction of insufficient transmission bandwidth of HD camera networks.
1, using advanced video compression standards
Actively adopt advanced video compression standards to ensure the best image quality with the least amount of data. At the same time, through the combination of image coding technology and intelligent technology, local coding can reduce the need for high-definition image transmission to a considerable extent. Network bandwidth.
At present, there are three mainstream compression formats, namely JPEG, MPEG-4, and H.264. JPEG is a compression of single-frame pictures. The effect of a single picture is best, but the network bandwidth resources occupied are large; MPEG-4 and H.264 are continuous compression between frames. Among them, H.264, the most popular compression format, has the highest compression efficiency, and the video data compressed by H.264 requires less bandwidth during network transmission.
2, provide dual stream support
While implementing high-definition local recording, dual-stream technology can reduce the bandwidth usage of remote transmission and ensure better local image quality. In the remote monitoring environment, the HD camera can provide a high bit rate code stream for local HD storage, such as 720P/1080P encoding, and a low bit rate code stream for network transmission, such as QCIF/CIF encoding, while taking into account local storage and Remote network transmission. According to the network bandwidth, the code stream format is flexibly selected to achieve local high-definition storage and the back-end low-stream network transmission. The stable operation of the transmission system can be ensured when the network resources available to the user are limited.
3. Improve the added value of smart technology
Intelligent technology can improve the monitoring efficiency, and the value it can bring is not limited to this. Through the coding and intelligent analysis front-end, the high-definition network camera with embedded intelligent analysis module can extract valuable information from the source and then transmit it to the background. It can reduce the transmission pressure and truly transmit effectively. The HD camera itself can analyze and judge the captured image and transmit the alarm signal to the back-end system. This is different from the way that the smart technology transmits the image to the back-end system and then analyzes the alarm by the software. The past method requires too much bandwidth and storage space, and is prone to false alarms due to loss of image signals during transmission. Since the HD camera has the most complete signal processing in the front camera, the accuracy of the alarm is greatly improved and the bandwidth can be reduced.
4, improve front-end caching technology
A well-designed front-end caching technology ensures that device images are not lost. HD cameras have limited data storage capabilities and rely on communication transport and back-end storage. We can prevent data loss in the event of a communication failure by designing a reasonable front-end caching mechanism. For example, in the design of a high-definition camera system, on-board memory or other storage devices can be selected and supported for offline operation. In the case of abnormal network interruption, the data can be temporarily stored locally, and then returned to the server after the network returns to normal. You can also use the network management technology to realize front-end caching when the network is temporarily interrupted. After the network is restored, the video data is automatically uploaded to ensure the integrity of the video.
5. Develop and comply with industry standards
It is necessary for all manufacturers in the monitoring market to unite and formulate some common norms, and seek common ground and keep small differences. At present, the emergence of standardization organizations such as Onvif and PSIA allows people to see the hope of standardization of video products and systems. The era of video surveillance "plug and play" is believed to be not far off.
Advantages of fiber transmission
Network transmission has a popular push for monitoring, but it is also constrained by network bandwidth. In large-scale long-distance engineering, the transmission performance is stretched. Based on the current megapixel HD 720P specification, the code stream is about D1 2 Times, the bandwidth reaches about 4M, and with 1080P calculation, the code stream is 5 times that of D1, and the bandwidth used is about 10M. Take 100M Ethernet as an example. Under the premise of ensuring smoothness, you can only carry about 5 HD images at the same time. However, if there are multiple users accessing the same video source, the occupied bandwidth will be larger. Switching to Gigabit Ethernet can take on dozens of channels. For small-scale high-definition monitoring systems, it can be effectively solved. For large projects, transmission performance will become a stumbling block.
In recent years, due to the rapid development of optical fiber communication technology, the cost of optical fiber transmission monitoring system has been greatly reduced, so the application of optical fiber and optical transceivers in monitoring systems is becoming more and more popular. As far as the author's investigation is concerned, optical fiber has been widely used in home optical fiber and office access networks, in the fields of home intelligence, office automation, industrial control networks, vehicle airborne and military communication networks. For high-definition video streams with high transmission bandwidth and high transmission distance, it is no longer a dream to realize high-definition surveillance in the era of optical fiber.
From the perspective of development, due to the characteristics of optical fiber transmission, optical fiber is the preferred transmission medium for transmitting digital high-definition signals. Fiber optic transmission also has the following advantages:
1, broadband, large traffic
The fiber optic has a wide frequency band and the theory can reach 3 billion megahertz, which guarantees the transmission bandwidth and quality of digital high-definition signals. It is unmatched by traditional copper cables. This makes fiber an ideal foundation for high-bandwidth data transmission.
2, low loss, suitable for long-distance transmission
The transmission distance of digital high-definition signals using traditional cables is only a few hundred meters, and optical fibers can transmit hundreds of meters or even tens of kilometers. It is especially important for reducing the cost of high-definition signal communication, improving reliability and stability.
3, anti-electromagnetic interference, no crosstalk interference, high confidentiality
The optical fiber is an insulator material, which is not affected by lightning interference in the natural world and changes in the ionosphere, and is not affected by electromagnetic fields and electromagnetic radiation, so the optical fiber provides a clearer signal than the copper wire; the light wave is difficult to transmit from the optical cable. Leaked out of the fiber. In this way, even if the total number of optical fibers in the optical cable is large, crosstalk-free interference can be realized, and the information transmitted in the optical fiber cannot be intercepted outside the optical cable.
4, light weight, small size for construction and maintenance
The tensile strength is good, the quality is small, and it is relatively small, so the optical cable can maximize the utilization rate of the wiring duct, and can reduce the installation problem as much as possible. We can analyze the advantages of fiber by the following figures. 1000 1km long twisted pair weighs 8000kg, while the larger 1km long fiber has a weight of only 100kg, which greatly reduces the need for maintenance. The need for expensive mechanical support systems, so fiber is better than copper.
5, scalability
The system with fiber as the transmission medium has a strong expansion capability, and the fiber has a wide passband and chemical corrosion resistance, and has a long service life. After investing once to form a physical link, you can upgrade and expand the system based on the original link. You only need to replace the device part without replacing the original fiber network. Greatly save system upgrade costs.
Fiber optic transmission technology provides unparalleled flexibility and scalability to meet the needs of the future. Fiber can provide much higher bandwidth than copper, which makes it more and more used for the transmission of video signals, computer signals and high-definition signals. Fiber optic technology provides the best solution for HD video surveillance.
With the continuous improvement and development of monitoring technology, HD network camera as one of the main directions of monitoring technology development, combined with optical imaging technology, intelligent analysis technology, network transmission technology, etc., brings new changes and continuously meets the needs of market competition. At the same time, it tends to be a perfect realization of oneself. It profoundly affects the field of surveillance technology and will profoundly change our way of life.
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