In many video systems still conventional coaxial cables are used to transmit the images of surveillance cameras – usually purely analog and therefore susceptible to interference. The only alternative so far offered only the complete transition to IP networks with Ethernet cabling to – along with all the advantages and disadvantages. Now an additional quality digital solution is available with the traditional wiring which can be further used.
Digital video in full HD at 1080p, in real-time, uncompressed and transfer of the highest quality, a standard coax connection – this is made possible thanks to the coming of television technology interface SDI.
Based on this “Serial Digital Interface”, which has become popular in the course of the conversion of many television stations to HD, an HD CCTV standard was developed that promises now in safety engineering broadcast quality.
Serial and Digital
Under the designation SDI, there are several standards adopted by the TV-bodies ITU-R and SMPTE for serial transmission of uncompressed digital video over coaxial cable.
The SDI standard specifies different transmission rates for different classes: Common are SD-SDI (standard SD-TV), ED-resolution (EDH) and HD-SDI (HD resolution). SD-SDI operates with a color subsampling of 4: 2: 2 and has a data rate of 270 megabits per second.
HD-SDI is suitable for high-definition television (HDTV) – the serial video stream here has a data rate of 1.485 Gbps. In the field of digital cinema, there is the DC-SDI (D-Cinema Serial Digital Interface). This interface is for uncompressed HDTV signals without color subsampling (4: 4: 4) designed and digitization of twelve bits.
The resulting data rate is 2.97 gigabits per second. The transmission of SDI signals via RG-59 coaxial cable with BNC connectors and an impedance of 75 ohms. The bridgeable distance lies with data rates up to 270 megabits at 300 meters, at higher data rates is 100 meters.
Broadcast Meets Security
Now this interface keeps in shape of HDcctv version called GDI (Grundig Digital Image) collection in the monitoring technology and is helping to solve fundamental problems. Until now video images that went high over the analog PAL standard, are digitally transmitted over a network – in spite of all this occurring weaknesses.
In the processing of HD video signals in a TV studio phenomena such as compression artifacts, latency or frame rate of less than 25 frames per second would have been intolerable, why not come here a transmission using IP network as an option into consideration. Of which can now benefit users in the security industry when implementing SDI in its existing coax infrastructure.
Full HD in Real Time
The video signal in an SDI system based on component video, here the brightness of the image and its two color components are separately encoded and transmitted serially. This is done at 1080p resolution with a high data rate of up to 1.5 gigabits per second.
The image here is in 16: 9 widescreen formats, so when using high-resolution full-HD monitors in this aspect ratio no black bars are formed and no image deterioration scaling necessary.
Thanks to the high bandwidth also is still room for additional digital data: For signals for triggering alarms or PTZ control can be easily transferred in real time in the same cable. This person tracking is about allowing a full HD PTZ dome without annoying latency.
SDI/GDI therefore are best suited for applications where live monitoring of the video is used with excellent image quality. As an example, mass events may be mentioned, in which the security forces have to intervene directly. Even for football stadiums, casinos, train stations and airports, the system are ideal because pursue targeted thanks to the high quality and real-time control and people can identify.
Without IT Hurdles
One of the advantages of the technique is that the HD video signals need not be interleaved in TCP / IP container. So there is no need to switch to a network system in order to overcome the limitations of the PAL standards.
Installers also do not need IT skills to install an SDI system – as was the complex IT and server technology for many still an obstacle for switching to IP systems. Rather, SDI is a point-to-point solution, which is characterized by an easy installation.
Thus there is the traditional procedure of installers very close: just exchange the existing CCTV cameras and video recorders against SDI devices. This also brings a profit in terms of safety. The transfer between the devices can not be manipulated; There is no susceptibility to “sniffing”, as is often the case in the network transmission.
Still can – if needed – a connection to a network produced. The easiest way is done by the DVR, where the signal compression and image processing takes place. This is – unlike IP models – deliberately not in the camera so that the SDI devices a long time can remain installed without obsolescence.
Fortunately, each SDI camera fits into any SDI infrastructure, so that you do not have to worry because compatibility issues – the default SMTP guaranteed cooperation. This can ultimately save not only time but also money.
The HD CCTV standard on SDI-based is now available in version 1.0, but will in future be further developed and adapted to the specific needs of surveillance technology.
The specially founded HDcctv Alliance cooperates with the Broadcast Panel SMPTE. The adjustments include bidirectional audio transmission and the availability of cables over 300 meters in length. Further additions are planned for the future. Including an integrated power supply via the coaxial cable, this reduces installation costs.