DVR-Based Analog CCTV Systems... become online on internet

DVRs were eventually equipped with an Ethernet port for network connectivity.

This introduced network DVRs to the market and enabled remote video monitoring using PCs. Some network DVR systems in use today enable the monitoring of both live and recorded video, whereas some allow the monitoring of only recorded video. Furthermore, some systems require a special Windows client to monitor the video, whereas others use a standard Web browser; the latter makes remote monitoring more flexible.

The network DVR system provides the following advantages:

·         Remote monitoring of video via a PC

·         Remote operation of the system

Although DVRs provided great improvements over VCRs, they also had some inherent downsides. The DVR was burdened with many tasks such as the digitization of video from all cameras, video compression, recording, and networking. Additionally, it was a “black box” solution, that is, proprietary hardware with preloaded software, which often forced the end user to source spare parts from one manufacturer, making maintenance and upgrading expensive. Virus protection was also difficult to implement. Although the DVR was often a

Windows-based machine, the proprietary interface did not allow for virus protection. In addition, the DVR offered limited scalability. Most DVRs offered 16 or 32 inputs, which made it difficult to cost-effectively build systems that were not multiples of 16, for example, systems with 10 or 35 cameras.

DVR-Based Analog CCTV Systems

By the mid-1990s, the video surveillance industry saw its first digital revolution with the introduction of the DVR. The DVR, with its hard drives, replaced the VCR as the recording medium. The video was digitized and then compressed to store as many days’ worth of video as possible.

With early DVRs, hard disk space was limited, so the recording duration was limited or a lower frame rate had to be used. Due to the limitations in hard disk space, many manufacturers developed proprietary compression algorithms. Although they might have worked well, end users were tied to one manufacturer's tools when it came to replaying the video. As the cost of hard disk space decreased dramatically over the years and standard compression algorithms such as MPEG-4 became available and widely accepted, most manufacturers gave up their proprietary compression in favor of standards — to the benefit of end users.

Most DVRs had several video inputs, typically 4, 16, or 32, which meant they also included the functionality of the quad or multiplexer.

DVR system provided the following major advantages:

• ·         No tapes and tape changes
• ·         Consistent recording quality
• ·         Ability to quickly search through recorded video

Early DVRs used analog monitors such as TV sets for showing video.

However, because the DVR made digital video available, it became possible to network and transmit the digital video over longer distances. This function was first addressed by connecting a phone modem to a serial port on the DVR. Later, the phone modem was built into the DVR itself.

Although the ability to monitor the video remotely via a PC was a great benefit, the actual functionality was not extremely useful because the bandwidth available with phone modems was too low, often in the 10- to 50-kbps range. That meant very low frame rates, low resolution, or highly compressed video, which made the video more or less useless.

VCR-Based Analog CCTV Systems

CCTV system involved the use of analog cameras that were connected to a VCR for recording video. The system was completely analog. The VCR used the same type of cassettes as those sold for a home VCR. Each camera needed its own coax cable to run from the camera all the way to the VCR. The video was not compressed, and when recording at full frame rate, one tape lasted a maximum of eight hours. Eventually, a so-called time lapse mode was incorporated into the VCRs to make the tape last longer. The time lapse mode enabled the recording of every second, fourth, eighth, or sixteenth image. That was how the video surveillance industry came up with such specifications as 15 fps (frames per second), 7.5 fps, 3.75 fps, and 1.875 fps, because these were the only recording frame rates possible in analog systems that used time lapse recording. If several cameras were used, quads became another important system component. A quad simply took inputs from four cameras and created one video signal output to show four different images on one screen; hence, the name “quad.” This invention made the system a bit more scalable but at the expense of lower resolution.

In even larger systems, multiplexers became commonplace. A multiplexer combined the video signals from several cameras into a multiplexed video signal. This made it possible to record even more cameras, often 16 on one device. The multiplexer also made it possible to map selected cameras to specific viewing monitors in a control room. Still, all equipment and all signals were analog. To monitor the video, analog monitors connected to a VCR, quad, or multiplexer.

Although analog systems functioned well, the drawbacks included limitations in scalability and the need to maintain VCRs and manually change tapes. In addition, the quality of the recordings deteriorated over time. The cameras, for a long time, were also black and white. Today, most analog cameras are in color.