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HD-SDI  and EX-SDI CCTV Video signal format.


Hi Definition- Serial Digital Interface.


SDI (Serial digital interface) has been about in the broadcast industry for quite a while for is fairly well established technology. Very high definition CMOS image processors have also been around for quite a while, commonly used in mobile phones. The problem for the CCTV industry was taking a high definition video signal and sending it down long lengths of copper cable without the signal degrading and then being able to record it at much higher resolutions than 960H.


A couple of years ago these problems were overcome and HD-SDI CCTV cameras and DVRs were introduced. The HD-SDI CCTV cameras produce a 1920 x 1080 pixel image and the HD-SDI CCTV DVRs record at 1920 x 1080 pixels. This is a total of 2.073,600 pixels or often referred to as 2.1 mega pixel. You can see that this is some 4 times higher than the very best composite video CCTV systems.


Because the video signal produced by the camera is not converted into analogue (CBVS cameras or AHD/TVI Hi definition analogue) or converted into H264 compression (IP cameras) for transmission down the camera cable the picture remains in its original format and resolution. It is also transmitted with no delay or latency and is transmitted in real time regarded as 25FPS (Frames per second)


Because of the nature of the video signal high grade RG59 coax or better specification coaxial cable must be used when installing HD-SDI CCTV cameras.


With the advent of AHD and TVI Hi definition CCTV and the improvements to IP CCTV systems many commentators are signaling the death of HD-SDI in the CCTV industry. This is not the case, AHD and TVI are not as good in both image quality and real time frame rates. IP still suffers from low frames rates and H264 blocking and the higher the resolution you get in IP cameras the worse these effects are.


One of the main critisiums of HD-SDI CCTV was the maximum cable run you could have before having to install an expensive signal booster. This was approximately 100m which in many cases was not relevent.


So the future of HD-SDI is EX-SDI, basically EX-SDI cameras when used with an EX-SDI DVR will be able to have cable runs upto about 300m without a booster. EX-SDI cameras and DVRs will be backwards compatible with HD-SDI cameras and DVRs. Also with the advent of 4K reslotion in the TV industry we expect much higher EX-SDI resolutions to be available in the not too distant future.




1)      Very high resolution images.

2)      True real time 25fps with very little latency (AHD & TVI only 12.5fps) IP as low as 5fps.

3)      Can be easily set up to be viewed over the internet or on a mobile device.

4)      Fairly robust tried and tested technology which when purchased from a reputable supplier/manufacturer should give many years of reliable service.

5)      I believe this technology will be around for a long time so service/repair will not be an issue.

6)      Not prone to electrical interference like analogue CCTV formats




1)      Must be cabled in High Grade RG59 coax

2)      Ready made cable kits are generally not available so you will need to make the cables up yourself. (With the new range of Screw terminal connectors this is quite easy)

3)      If a camera cable run is over 100m then an SDI signal repeater must be used. These are expensive costing about £100 each.


Please check the specification of any HD-SDI DVR before you purchase. There a quite a few models that will not record at 25fps or will not record all channels at 1080p (1920 x 1080) resolution some only record at 720P (1280 x 720) resolution. Only buy HD-SDI cameras that use Panasonic or Sony CMOS image processors. Beware if the price of an HD-SDI camera looks too good to be true.


Respectway Limited, Merlin House, Station Road, Brompton-on-Swale, North Yorkshire, DL10 7SE, Tel: 01748 811991  Email. sales@cctvfirst.co.uk
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