Signal standards and parameters

Video signal used in CCTV is called VBS (video, blanking & syncs, or video baseband signal) and CVBS (composite/color video baseband signal).

VBS is composed of synchronization / blanking impulses and luminance information, CVBS additionally comprises chrominance information. Luminance carries information about image brightness, chrominance informs about colors in the image. Synchronization impulses are in fact combined signals of horizontal and vertical deflection, which synchronize monitor with the camera.

The standard composite video signal has 1V_p-p amplitude (peak-to-peak). The input and output impedance of each device processing video signal should be 75 ohm. It is a standard value commonly used in television/video technology, so that it is possible to use some universal devices. The example may be the former use of video cassette recorder, or real-time monitoring on regular TV set equipped with audio/video input. Of course, application of consumer electronics equipment in professional CCTV installations is generally not acceptable. It does not guarantee continuous operation nor the optimum quality.

Applied standards

Due to established principles and image quality, the frequency range of video baseband signal is 25 Hz to at least 5.0 MHz. The set of all requirements for the video signal is called a television standard. The standard defines, among others, polarization, number of TV lines (TVL), image frame rate, horizontal scanning frequency, vertical scanning frequency, channel raster, video signal bandwidth and frequency of audio carrier. Analog CCTV systems usually do not use audio features.

The standard used in Poland is PAL D/K, most countries in West Europe use PAL B/G. With regard to video signal parameters, the both standards are practically identical. Generally, but not quite correctly, the B/G standard is called CCIR, and the D/K - OIRT. United States and some Asian countries use different standard, called EIA or NTSC. Cameras using that standard are not compatible with devices designed for European standards.

It should be remembered all devices in a system must operate in the same standard and system. Information about the standard and system can be found in the instructions for the device, usually it is also placed on the device.

While small, local video monitoring systems are still built basing on analog cameras and DVRs (with digital recording on HDDs), larger systems or monitoring systems in dispersed locations have to employ IP technology. Modern buildings with embedded modern communication systems allow to easily implement IP CCTV solutions. It provides tremendous opportunities not only for transmitting and recording of multiple digital streams of video and audio, but also for sophisticated analysis of the data (unusual activity, appearing and disappearing objects, counting of objects, smoke and fire detection etc). An overwhelming advantage of IP CCTV technology is also the possibility of using megapixel cameras, including transmission and recording of their high-definition images.

IP is the acronym of the Internet Protocol, the most popular protocol used for communication in computer networks and the Internet. IP camera is a device producing digital video stream that is transmitted via wired or wireless IP networks. It can be viewed and/or recorded even in most remote locations in the network.

Video surveillance systems based on IP CCTV devices need adequate IP networks for transmitting video data and providing communication among the devices and computers or transcoders.

IP CCTV devices send video or video and audio in the form of data stream, usually compressed in MPEG-4 (SP, ASP, AVC/H.264) or MJPEG format. Compression limits the required band. However, the quality of video and audio strongly decreases with higher compression ratios. Some applications may require full resolution (e.g. megapixel cameras) or maximum frame rate - in such cases the required bandwidth can be very wide.

More on the requirements for IP networks for video surveillance systems you can read in the article LAN for IP video surveillance.

The article Architecture of video surveillance systems based on IP networks discusses the basic configurations of IP CCTV systems.

IP CCTV system based on server - client architecture