Security video surveillance has been developed in China for more than ten years, and various new products and technologies are emerging one after another. The current general trend is toward full HD, high bandwidth and intelligent. Around 2007, the security industry began to use IP cameras on a large scale, so that security video surveillance gradually entered the high-definition hall; in 2011, SDI high-definition interface entered the security market, making HD implementation an additional way. In the 2011 Shenzhen Expo, various manufacturers pushed high-definition products and high-definition technology, and “HD†became the hottest topic in video surveillance.
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In analog monitoring systems, video transmission is relatively easy: in the range of a few hundred meters, the use of ordinary coaxial lines can achieve better quality transmission; even at longer distances, the use of video optical transceivers can achieve thousands of multi-channel video The transmission of meters distance. In the high-definition era, the situation is completely different. For example, the HDMI video signal of the FULL-HD1080P format output from the back-end recorder, decoder, and matrix, if using ordinary copper cable transmission, the distance is no more than ten meters; from the front camera The output HD-SDI video signal, if using ordinary coaxial transmission, the distance is generally less than 70 meters, therefore, the transmission restricts the development of high-definition video surveillance. If HD video does not have a good transmission, even with HD cameras, HD displays are difficult to achieve true HD images.
Table 1:
Note: Due to the difference in the quality of the transmission medium or the influence of the external environment, the actual transmission distance and effect are slightly different.
It is gratifying to note that various transmission products have appeared quietly on the market, which better solves the problem of high-definition transmission. Here is a brief introduction to everyone:
1. At the front end (HD-SDI camera to intermediate storage control device recorder matrix encoder): a, within 70 meters (due to wire quality and environmental impact, the actual distance is deviated) can use 75-5 coaxial cable. b. In many cases, it will be more than 70 meters. At this time, HD-SDI repeaters can be used, and each repeater can extend the transmission distance by 150-200 meters. c. When the transmission is far away, the SDI optical transceiver can be used, which can realize the transmission of up to several tens of kilometers. When the RS485232 control signal needs to be transmitted, the SDIRS485 optical fiber transmitter can be used.
2. In the intermediate storage control part (HD-SDIDVR and SDI matrix, etc.), use DVR to realize SDI video storage, and realize connection with Ethernet. If you need to implement multi-input, multi-output video exchange, then you need to use the SDI matrix. However, existing general displays (monitors) do not support SDI. There are several solutions at this point: one is to use SDI signal converter to convert SDI to HDMI, DVI, VGA converter; another way is to use multi-format input and output matrix, which the industry calls a hybrid matrix. The hybrid matrix can realize the input of various signals (analog, HD: CVBS, VGA, HDMI, DVI, YpbPr), the output of high-definition signals (SDI, HDMI, DVI, etc.), that is, the analog camera signal, digital HD SDI Signal and VGA, HDMI, DVI and other computer video signal mixed input, output in SDI, HDMI, DVI format.
3. At the back end (matrix DVR to display device), you need to transmit HDMI, DVI or VGA signals. The VGA signal can transmit about 15 meters, but it is an analog signal, does not support true high definition, and has a tendency to be gradually replaced by HDMIDVI. HDMIDVI1080P video signal, if using ordinary copper cable transmission, the distance is less than 10 meters; once the distance exceeds 10 meters, it will face video transmission problems.
In addition, in network monitoring, the NVR or decoder that implements storage also outputs HDMI or DVI. If they are longer than the display device, they will also face transmission problems.
In the current monitoring project, more and more large-screen displays are used. The large-screen display is not only used to display surveillance video, but also to display computer signals, DVD signals, etc., and can also be applied to command and dispatch centers and video conferences. The transmission problem highlighted by the large-screen display project is particularly obvious: signal sources such as matrix, DVR, decoder, etc. are generally installed in the computer room, while large screens are generally installed in conference rooms, halls, etc., often between 30 meters and 200 meters. The distance, ordinary copper cable can not solve this transmission problem.
Common products for solving HDMIDVI long-distance transmission are as follows:
Special copper cable (built-in automatic equalizer), can transfer 1080P HDMIDVI about 40 meters.
The network cable transmitter, using the ordinary CAT-6 network cable, can transmit 1080P HDMIDVI about 50 meters.
Fiber optic transmitter
The fiber optic transmitter using 4-core multimode fiber can transmit 1080P HDMIDVI about 500 meters;
The optical fiber transmitter with 1-core multimode fiber can transmit 1080P HDMIDVI about 300 meters;
The fiber optic transmitter with 2-core single-mode fiber can transmit 1080P HDMIDVI about 1500 meters.
HD transmission product comparison:
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