This article comes from China Security Industry Network (. Com.cn)

Introduction: SDI is a serial digital interface, which is a digital non-compression technology. After the analog-to-digital conversion of video, there are two ways to go—compressed or uncompressed. IP surveillance takes a compressed path. The benefit is a large amount of compressed bandwidth, which makes it possible to transmit video over IP networks and video data. The storage capacity is not massive, but the cost is to bring down the quality of the video, control the existence of delays and openness brought about by the hidden dangers. In the past two years, SDI technology originated from broadcasting and television has gained importance in the field of video surveillance and has been initially applied.

SDI is a serial digital interface, which is a digital non-compression technology. After the analog-to-digital conversion of video, there are two ways to go—compressed or uncompressed. IP surveillance takes a compressed path. The benefit is a large amount of compressed bandwidth, which makes it possible to transmit video over IP networks and video data. The storage capacity is not massive, but the cost is to bring down the quality of the video, control the existence of delays and openness brought about by the hidden dangers. If you take the uncompressed path (ie digital non-compression technology), there are many technical standards, such as common HDMI, DVI, and SDI. As the name implies, the digital non-compressed video technology is not compressed after analog-to-digital conversion, but is encoded in a special way (this encoding is different from compression encoding, and there is no lossy compression process). The advantage of non-compression is the maximum fidelity of the video quality, while there is almost no delay, and the cost is the enormous amount of video signal data.

SDI is currently divided into three standards according to video resolution and frame rate: 1SD-SDI is standard definition SDI, mainly for SD resolution, 25 frames per second or 30 frames (resolution is PAL and NTSC, the same below). The video bandwidth after analog-to-digital conversion is approximately 250Mbps (or 360Mbps for 16:9); HD-SDI means high-definition SDI. This standard is mainly aimed at a resolution of 1080P, a frame rate of 25 or 30, and analog-to-digital conversion. After the amount of data is 1.485Gbps; 3G-SDI, high-definition frame rate SDI, resolution is still 1080P, but the frame rate increased to 50 or 60, the amount of data after the analog-to-digital conversion is 2.97Gbps. It can be seen that the amount of original data that is not compressed after video analog-to-digital conversion is very large. If it is not compressed, such a large amount of data cannot be carried by the IP network at all. At the same time, if these data are directly stored, the storage capacity will be very high. amazing.

Since SD video is almost all analog, SD-SDI is not significant in the surveillance field, but 3G-SDI data is too large. Such a high frame rate is not necessary in the surveillance area. Therefore, 3G standard SDI is unlikely to be widely used. For now, what may really open up in surveillance is HD-SDI, which provides high-definition video with a resolution of 1080p while preserving all the details of the video at the same time. Equivalent to traditional analog systems.

Among the numerous digital video non-compression standards, SDI is the most promising or most likely to be used in the surveillance field. The main reasons are: HD-SDI uses a high-grade coaxial cable to achieve a non-relay transmission distance of 100 Around meters, it is the furthest among many video non-compression standards, which brings convenience for on-site use. The specific monitoring system based on HD-SDI has the following advantages:

The cable uses high quality coaxial cable and the connector uses a high quality BNC connector. These are all compatible with the previous analog monitoring system. The original analog monitoring system can be upgraded to an SDI system as long as the transmission line is reserved. Of course, almost all the equipment in the original analog system must be simultaneously updated to the corresponding SDI equipment, such as SDI. Front-end, SDI optical transceiver, SDI video distributor, SDI matrix, SDI-DVR, etc. The newly constructed system structure is almost completely similar to the original traditional simulation system, providing great convenience for the design and construction of the project.

Without distortion, HD-SDI does not transmit video data in a packetized manner on the network as in the case of IP systems. HD-SDI video is transmitted over coaxial cable with uncompressed signals, which is stable and reliable without distortion.

High-definition real-time image, SDI has not been compressed and packaged in the video production and transmission process and decoding process, does not produce the delay of IP high-definition image, especially suitable for real-time monitoring of the occasion, such as casinos, road traffic;

Multiple transmissions can be made on the coaxial cable. The coaxial cable can not only transmit video, but also transmit audio. In this way, the video matrix and audio matrix in the analog system can be combined. Meanwhile, the SDI standard also supports the transmission of control signals on the coaxial cable, and the control signal of the future PTZ. It can also be transmitted via coaxial cable, without the need for laying control cables, and power is also very likely to be transmitted over coaxial cables. In this way, it is truly possible to transmit a variety of signals over a single coaxial cable, which saves wiring costs.

Provides high-quality video signals for intelligent video analysis. Uncompressed high-definition video signals will greatly improve the accuracy of intelligent video analysis.

It has the potential of signal security and system openness similar to analog systems.

The biggest problems currently existing in HD-SDI systems are the following:

1. The front-end lightning protection does not solve the problem that SDI is from the field of broadcasting and television, and is mainly used in indoor environments. There is no precedent for large-scale use in the field. The formulation of related standards does not consider the application in industrial environments. The related lightning protection technology was not available before. reserve. SDI cables transmit high-frequency digital signals. The principle and design of lightning protectors are completely different from those of analog video. At present, it should be said that there are still no good solutions. To solve this problem, you can consider using optical fiber to solve the problem. Cameras installed in the outfield can be connected to SDI optical transceivers nearby. Further, SDI front-ends can directly output video signals through optical fiber ports. Once optical fiber transmission is used, interference and lightning protection are basically solved. Even if not for outdoor projects, the HD-SDI system can be used for indoor projects such as subways.

2. Cable grade HD-SDI high-definition video signal can best be transmitted on a dedicated SDI cable to ensure the best effect of the video signal, but dedicated SDI cables including connectors are expensive, in actual projects, if All the use of dedicated SDI cables will increase the construction cost, and after actual testing, the use of high-grade coaxial cables and BNC heads can basically guarantee the video effect. Moreover, as long as SDI is used widely, the prices of related auxiliary materials will definitely drop sharply.

3, storage solution As mentioned above, high-definition uncompressed video signal data volume is very large, with such a data amount to directly store the cost is quite large, so from practical considerations, the video storage still needs to be compressed, specifically Said that you can use SDI-DVR can also be solved with SDI encoder with NVR. According to the actual choice of project flexibility. Even so, the advantages of the HD-SDI system over the HD-IP system are obvious: on the premise of maintaining the same quality of storage capacity, the HD-SDI system fully excels in real-time control. At the same time, the HD-SDI system is completely controlled. Delay, so you can see what you see and save without losing important videos.

4. Matrix scale The system scale of the current SDI matrix is ​​subject to the upstream chip manufacturers. At the same time, the product design and manufacturing technology and the analog matrix are also very different. Therefore, the large-capacity modular expandable SDI matrix is ​​rarely available today. It is a small-scale (64×16, etc.) product. However, this is not a problem. If the SDI system can be widely used, chip and design technology will soon be a breakthrough, large-scale SDI matrix will soon appear.

In a real project, HD-SDI systems can be used to form a single system, but it is more likely to be used in conjunction with other systems or as a node in the entire large-scale monitoring network.