The Evolution of Video Surveillance Systems
Video surveillance, more commonly called CCTV (closed-circuit television), is an industry that is more than 30 years old and one that has had its share of technology changes. As in any other industry, end users' ever-increasing demands on the products and solutions are driving the changes, and evolving technologies are helping to support them. In the video surveillance market, the demands include:
- Better image quality
- Simplified installation and maintenance
- More secure and reliable technology
- Longer retention of recorded video
- Reduction in costs
- Size and scalability
- Remote monitoring capabilities
- Integration with other systems
- More built-in system intelligence
To meet these requirements, video surveillance has experienced a number of technology shifts. The latest is the shift from analog CCTV surveillance to fully digital, network-based video surveillance systems.
Video surveillance systems started out as 100-percent analog systems and are gradually becoming digital. Today's systems, using network cameras and PC (personal computer) servers for video recording in a fully digital system, have come a long way from the early analog tube cameras, which were connected to a VCR (videocassette recorder).
In between the fully analog and fully digital systems, there are several solutions that are partly digital, that is, systems that incorporate both digital and analog devices. This has led to some confusion in the video surveillance industry today, as some talk about a "digital" system to mean analog cameras that connect to a DVR (digital video recorder), whereas others use the term to describe a network video system with network cameras. Although there are digital components in both systems, there are some very important distinctions to make between each of the systems.
The sections below outline the evolution of video surveillance systems. Different system configurations, from fully analog to fully digital, are explained, along with the benefits of each configuration. The systems described in Sections 2 and 3 constitute partly "digital" video systems. Only the systems described in Sections 4 and 5 are true network video systems in which video streams are continuously being transported over an IP network, providing full scalability and flexibility.
1. VCR-Based Analog CCTV Systems
The traditional analog CCTV system involved the use of analog cameras that were connected to a VCR for recording video (Figure 1). 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.
Figure 1. Diagram showing a classical analog video surveillance system.
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.
2. 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 (Figure 2). The video was digitized and then compressed to store as many days' worth of video as possible.
Figure 2. A surveillance system with analog cameras connected to a DVR, which includes the quad or multiplexer functionality and provides digital recording.
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. Hence, DVRs replaced the multiplexer as well as the VCR and thereby reduced the number of components in the CCTV system.
The introduction of the 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.
3. Network DVR-Based Analog CCTV Systems
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 (Figure 3). 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.
Figure 3. A system that shows how analog cameras can be networked using a network DVR for remote monitoring of live and recorded video.
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.
4. Video Encoder-Based Network Video Systems
The first step into a networked video system based on an open platform came with the introduction of the video encoder, which is also often called a video server.
A video encoder connects to analog cameras and digitizes and compresses the video. It then sends the video over an IP network via a network switch to a PC server that runs video management software for monitoring and recording (Figure 4). This is a true network video system because the video is consistently sent over an IP network. In essence, the tasks previously performed by the DVR are now divided up - with the digitization and compression being done by the video encoder and the recording by the PC server - thus providing better scalability.
Figure 4. A true network video system, where video is continuously transported over an IP network. It uses a video encoder as the cornerstone to migrate the analog security system into an open IP-based video solution.
A video encoder-based network video system has the following advantages:
- Use of standard network and PC server hardware for video recording and management
- Scalability in steps of one camera at a time
- Possibility to record off site
- Future-proof because the system is expanded easily by incorporating network cameras
4.1 NVRs and Hybrid DVRs
Alternatives to the open platform (based on a PC with video management software installed) are also possible with the availability of different types of NVRs (network video recorders; Figure 5) and hybrid DVRs. An NVR or hybrid DVR is a proprietary hardware box with preinstalled video management software for managing video from video encoders or network cameras. The NVR handles only network video inputs, whereas the hybrid DVR can handle both network video as well as analog inputs in parallel. The benefit of using an NVR or hybrid DVR is the ease of installation because the recording and video management functionalities are made available all in one box - similar to a DVR. The NVR or hybrid DVR solution is popular in smaller systems with 4 to 16 cameras. However, it also maintains some of the drawbacks of the traditional DVR. NVRs and hybrid DVRs use a proprietary platform that is more expensive to purchase, maintain, and upgrade, and they are often difficult to maintain on a corporate IT network.
Figure 5. The NVR is a hardware box with preinstalled video management software that makes installation simpler but lacks the flexibility of an open-platform system based on a standard PC server.
5. Network Camera-Based Network Video Systems
A network camera, also commonly called an IP camera, is, as its name describes, a camera with an IP network connection. In a network camera-based network video system, video is transported over an IP network via network switches and is recorded to a PC server with video management software installed (Figure 6). This represents a true network video system. The system is fully digital because no analog components are used.
Figure 6. This diagram shows a true network video system where videos from network cameras are continuously transported over an IP network. This system takes full advantage of digital technology and provides consistent image quality from the cameras to the viewer at any location.
One of the greatest benefits of a network camera is that once images are captured, they are digitized once inside the camera and remain digital throughout the system, which provides for high and consistent image quality. This is not the case with analog cameras. Although most analog cameras today are called "digital," they have an analog output, and this can lead to some confusion. Analog cameras do digitize captured images to provide image-enhancing functions. However, these images are then converted back to analog video. It is important to know that with every conversion from analog to digital, or from digital to analog, there is some loss of video quality. Additionally, analog signals degrade when transported over long cables and over time if stored on tape. Therefore, video ideally should be digitized once and stay digital throughout the system.
The benefit of using an IP-based network is that one can use the network for more than just transporting video. IP networks provide a means for several network cameras to share the same physical cable. In addition, the network can carry power to network cameras and information to and from the outputs and input contacts of the cameras. It can also carry two-way audio, as well as pan, tilt, and zoom commands if a camera has that functionality. Furthermore, an IP network enables network cameras to be configured remotely and allows video and other data that are sent over the network to reach virtually any location with no degradation in quality.
All in all, the network provides an extremely flexible and cost-efficient medium for all communications within a network video surveillance system. The scalability of network video provides opportunities to build video surveillance systems with hundreds or even thousands of cameras.
A network camera-based network video system provides the following advantages:
- Ability to use high- resolution (megapixel) cameras
- Consistent image quality, regardless of distance
- Ability to use Power over Ethernet and wireless functionality
- Full access to functionalities such as pan, tilt, and zoom; audio and digital inputs and outputs over IP, together with video
- Camera settings and system adjustments over IP
- Full flexibility and scalability
Although a network camera can be compared to an analog camera attached to a video encoder, a network camera can offer many more functionalities that extend beyond the capabilities of a system involving an analog camera and a video encoder. Because a network camera has built-in computing power, it opens up the possibility for video intelligence, also called video analytics, at the edge of the system, that is, within the camera. This is expected to be the next big trend within video surveillance because there is a necessity to manage and analyze video effectively, especially in large systems.
The network camera is a key driver in the network video revolution. Network cameras have fully caught up with analog camera technology and now meet the same requirements and specifications. Moreover, network cameras surpass analog camera performance in many important areas, such as image quality, resolution, and built-in intelligence.
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