Maragrete Betger, Export Manager of Grundig, explains HD - SDI.

12 May 2012

Despite the high-profile attention IP CCTV has received in recent years, many new CCTV installations still use analogue technology. Countless installers have found that the superior image quality and functionality IP CCTV systems claim to offer, do not outweigh the straight-forward installation and minimal IT support associated with analogue systems. We have asked Margarete Betger, Export Manager of Grundig which designs and manufactures analogue, IP and HD CCTV security systems, to interpret this trend. We have also asked her to explain why the new HD CCTV technology is proving so popular.

Installers have shown they prefer the simplicity of connecting a CCTV camera directly to a DVR using conventional RG59 coaxial cable. They also do not want to have to protect the entire CCTV system from network security threats. At Grundig, this is something we have taken into account when developing our products.

High Definition - Serial Digital Interface (HD-SDI) CCTV is a major breakthrough in the security industry. It is a digital video transmission solution designed for a coaxial cable infrastructure, combining digital CCTV quality with simple, analogue-style installation and support. HD-SDI enables the transmission of uncompressed digital video, in real time (25fps), over RG59 coaxial cable and delivers a significantly higher image quality than IP. It even enables installers to offer a digital upgrade to analogue systems, re-using the existing coaxial cable infrastructure to save money. Not surprisingly, HD-SDI CCTV is proving to be extremely popular with installers.

The broadcast and security industries unite

HD-SDI is derived from the television broadcast industry. Just as HD television has been replacing standard television in domestic applications, HD CCTV has been doing likewise in video surveillance applications. When high-quality video is transmitted across a network, compression artifacts and latency can occur, due to the bandwidth limitations of IP networks. Reducing frame rates helps to address these issues, but frame rates below 25fps are no longer real-time and video quality is still compromised. Within the broadcast industry, latency and artifacts are simply not acceptable, so IP network technology has never been an option. Instead, the broadcast industry developed SDI, its own standard for digital transmission using coaxial cabling. The SMTP standard has also been used within SDI development to ensure system compatibility between manufacturers. It is this SDI standard that the security industry is now adopting for HD CCTV and one we have embraced at Grundig.

SDI data rates, resolutions and transmission distances

The SDI standard has categorized data rates for the transmission of uncompressed digital video over RG59 coaxial cable. Standard Definition – SDI (SD-SDI), which approximates to D1 resolution (720 x 576 pixels), uses colour-subsampling of 4:2:2 with a data rate of 270 megabits per second. HD-SDI, sometimes described as 1080p (progressive scan), equates to 2 megapixel resolution (1980 x 1080pixels) with a data rate of up to 1.485 gigabits per second. 3G-SDI, originally developed for digital cinema applications, is designed for uncompressed HD signals without colour subsampling (4:4:4) and twelve-bit digitalization. The resulting data rate is 2.97 gigabits per second.

There are now many surveillance cameras with SD-SDI, HD-SDI or even 3G-SDI connectivity. Transmission distances are similar to IP, ranging from 100m for HD-SDI down to 70m using 3G-SDI. However, developments in SDI-specific, fibre optic transmission systems are extending transmission distances to many kilometers.

Full-HD in real time

Within HD-SDI the image is presented in 16:9, widescreen format, meaning no black bars appear on high-resolution, full-HD monitors. HD-SDI is of considerably higher resolution than D1 and the IP-based, 1.3 megapixel (1280 x 1024 pixels) cameras commonly available. However, whereas IP CCTV solutions use video compression techniques to reduce video data size before transmission, HD-SDI uses no compression at all, so quality is always optimized.

Where to use a network

The “spare” bandwidth available in HD-SDI transmission enables additional data to be carried within the same coaxial cable as the video signal. This can include alarm triggers, alerts, PTZ telemetry control and live people tracking.

HD CCTV is ideal for applications where a site is monitored in real-time. Examples include football stadiums, casinos, train stations and airports. System control, tracking, identification of specific individuals and the initiation of an immediate response to serious incidents are all enabled.

An HD CCTV system can still be connected to an IP network for remote access, DVR software updates, remote maintenance or multi-site control and management. However, this is best done at the DVR, after the HD-SDI signal and image processing has taken place.

Despite CCTV manufacturers, including Grundig, developing IP CCTV equipment that is easily set-up by installers, the IP CCTV system itself is rarely where problems occur. Securing the video data within an open IP network (LAN or WAN) requires IT expertise beyond the comfort zone of most security installers. Most IP network environments need advanced security settings to protect data. By comparison, SDI is a closed system, with limited external access. This makes it intrinsically safe, far simpler to protect, ideal for installers and very effective in security applications.

Future developments

At Grundig, we believe HD-SDI CCTV will continue to evolve and adapt to the particular needs of surveillance technology. It could even reach the point where it supersedes IP CCTV. The HD CCTV Alliance is working with the broadcast SMPTE committee overseeing developments such as bi-directional audio, the extension of coaxial cable transmission distances to 300m or more and power over coaxial solutions. At its core, HD-SDI combines all the best parts of IP and analogue CCTV systems, to produce a high-quality, cost-effective new CCTV solution which is installer–friendly and secure.