The Apples and Oranges of CCTV Systems.

Admittedly, too many articles discussing the merits of Digital CCTV technologies over Analogue technologies in trade publications today are not expressed in layman's terms but rather technical jargon.

Too many of the articles rely on misinformation and hype, usually weighted in favor of a manufacturer's product, rather than on the important issues such as ease of use, operational considerations, cost effectiveness or adaptability to an existing system.

Many manufacturer's rep's are relying on customers' ignorance and are hoodwinking them rather than educating them and allowing them to make an informed decision.

Take for instance this scenario; a potential user of Digital Video Recorders (DVRs) had requested a quote from each of two providers, stating they would be recording from 32 cameras simultaneously for 30 days. The two suppliers' price quotes differed by 30%.

Based solely on price, the end user was about place their order with Company A, thinking they would be getting the better deal. Fortunately, Company B, who had the higher quote, contacted them prior to their committing to their purchase and asked for the opportunity to explain their offer, being certain their solution could not be that much more expensive than the other.

Evaluation showed that Company B had quoted 3 x 120GB hard disk drives to achieve the requirement of the end user. They had also quoted a refresh rate of 3.125 frames per seconds. Company A, however had quoted they could store 32 cameras for 30 days on a 20Gb hard disk drive, an impossible task considering current technology would not allow this at the same refresh rates as quoted by Company B

By carefully examining the quotations, it was found in small print on Company A's quotation that their storage estimate was based on a recording rate of 1 frame every 2 minutes. A lot can happen in a 2 minute interval in a security situation so effective historical analysis would not have been possible utilizing this solution.

Upon seeing this, the customer asked Company A to revise their quote based on the refresh rate of 3.15 frames per second. They did this and it was found that their DVR was not capable of supporting hard disks with sufficient capacity to meet the specification. To meet the requirements, Company A was forced to utilize and external archive unit which drove up the price of their offer to almost twice that of Company B's original offer.

This is typical of what we call “spec sheet selling�? which seems to be prevalent in the CCTV industry at the moment, and seems to follow the introduction of new technology in any market where a buyer can be hoodwinked by misinformation. This process forces customers to learn by their mistakes which can be a costly option.

This article is intended to cut through much of the hype surrounding DVRs and provide guidance to those considering adopting this exciting technological advance to enhance their security operation.

To reiterate, video images can be saved on a hard disk by using Digital Video Recorders (DVRs), instead of using videotapes that degrade with use and have many moving parts. Digital video techniques enable enhanced and more efficient search facilities. It is easy to search the video image stored on the hard disk drives via time and date criteria as opposed to the time consuming method of rewinding and viewing video tapes. In addition, multiple copies of recordings can be produced without degradation. Ease of distribution is acquired through the transmission of images over LAN/WAN technology, and the adoption of video player software into PC operating systems allows the viewing of video clips without proprietary viewing software.

In the issue of sending video images over the network, there are several factors to consider. A key factor is the bandwidth of the computer network. If a bandwidth is limited, the amount of information being sent over the network must be reduced, either by longer refresh intervals or lower image quality. The factors affecting the file size are: Compression Algorithm, Refresh Rate and Resolution. Compression is the amount of redundant video information that can be stripped out of a video image before storage and transmission. The higher the compression, the more information is lost. There are basically two methods of compression to enable the transmission of high-quality video over a network. Either a complete image is transmitted every time (JPEG, Wavelet) or a reference image is transmitted and updated little by little (MPEG, H263) until a major change requires that a new reference image should be transmitted. Either method is suitable depending on the application.

What does this mean to the user of the system? Different compression techniques and rates will affect the storage requirements and the bandwidth utilization. This, in turn, will affect the capital cost and cost of ownership of the system.

Refresh rates refers to how often the image is updated and are generally quoted in Frames per Second (fps). A twenty-five frames per second rate provides real-time live video. Fps may also refer to Fields per Second which adds to the confusion in seeking DVR capabilities since there are two fields in each frame. Some manufactures will quote 50 fps giving the unsuspecting buyer that this unit has twice the refresh rate of a 25 frames per second unit. Pictures or Images per second are substituted for Frames as well, contributing further to the confusion. The refresh rate has nothing to do with the quality of the image: it only affects the smooth movement of objects within the field of view.

There is a high cost however in capturing 25 frames per second real-time video. The more frames that are recorded the larger the file size, which requires more storage devices and utilize increased bandwidth on a network. To compensate for this, many (almost 75%) of the units installed are throttled back to a level that provides a good compromise between usability and cost overhead. A standard that most companies are utilizing is 3.125 fps. This provides adequate surveillance while reducing storage requirements and minimizing the impact on a network. However, potential users are still requesting 25fps within specifications, without realizing the impact, because this is the information they have been given by less than scrupulous suppliers.

For example our eyes and brain can not necessarily process the difference between 12.5 and 25 frames per second. Consider the early days of animated cartoons to get an idea of what this means. Early animations were produced at 15 cells per second as opposed to 25, thus reducing time and cost to produce an animated film. When viewing the animations a person saw these as real time moving pictures as the receptors in their eyes could not process the information quickly enough to see the difference.

It is important to analyze the differences between the refresh rates when evaluating a system. Do this by visiting the dealer and comparing several cameras all set up at different refresh rates and all looking at the same view. When doing so ensure that there is movement in the field of view, which is likely to represent your actual conditions. By doing so, you should be able to settle upon a refresh rate that meets your operational requirements. You should also request a quotation based on two scenarios, one at the optimum refresh rate and another at a rate which you would be prepared to accept. Set some parameters for the quote, such as 32 cameras, all recording at x fps with storage for 30 days.

Resolution is the measure of image quality and is measured in pixels. The higher the image quality the more data, so therefore, images with a lot of data will take longer to transmit, utilize more network bandwidth and will require more space on the hard disk to store. Consider the amount of detail you need to capture on any particular camera when making your choices.

Digital CCTV recorders are basically a PC with 1 or more hard disks included for the storage of the video images. Storage requirements will vary widely depending on compression algorithm, the amount of compression selected, the refresh rate utilized and the resolution adopted. As specifications are increased more hard disks will be required.

Hard Disks are now quoted in terms of the number of transactions written to them before failure, rather than the length of time before failure. Since information is continuously being written to the disk/s recording video is a very transaction intensive process. The law of averages dictates that the more disks one uses for storage, the more likely it is that one will fail.

Because the trend seems to be that the hard drive is the common point of failure it is important to select a DVR that has the largest capacity disk drives available as it is better to have fewer large disks than more small capacity disks. You should also consider DVRs with easily removable disks as well, rather than those that would require a complete strip down to replace a disk.

Consider also if multiple disks in a DVR are treated as a single volume or not. In such instances as this, if one disks should fail, information on all the disks would be lost. Some manufacturers treat each disk as a separate volume so if one disk should fail only the information on that disk would be lost while the information on the others would remain intact. To combat the disk failure issue, many manufacturers utilize RAID storage devices, which will allow for disk failure without the loss of information.

Digital Video Recorders can store only a limited amount of information, limited by the number of hard disks mounted within the unit. Although some DVRs can accommodate up to 1 terabyte of hard disk space, this will soon fill up. For this reason, many DVR manufacturers set up two areas of storage, one being for event driven “locked�? video, the other being for continuously recorded video.

The system is continuously recording, or storing, the video and when an “event�? occurs it will “grab�? the video associated with that even from the cache, according to pre and post alarm video configuration, and place it in a locked file. These files cannot be overwritten unless the operator manually purges them. The cache is overwritten on a first in first out basis. Eventually though the disk will fill up with locked video unless there is a purging from time to time as the ratio of locked video space to free space on a disk is dynamically allocated.

If the user wishes to access any of the recorded information at a later time, it will be necessary to archive the video. Information can be archived to two types of media, either tapes (video juke boxes) or arrays of disks. Tape which is bordering on being antiquated, tends to be slow in terms of information throughput and selection and loading of the tape containing the relevant clips and contain many moving parts and so require regular maintenance, but they are the cheaper solution. On the other hand, disks offer almost immediate access to video clips but at greater cost. As Hard Disk Drive costs are continually coming down and sizes are growing this difference in cost is becoming smaller and smaller.

Most DVRs rely on these being located next to and attached to the field DVRs. If for example, the customer has 3 digital video recorders they would require 3 archive storage devices. Also available are central archiving capabilities, meaning that video images from remote DVRs are transmitted across the network and stored centrally on either tape or disk. It is now possible to store petabytes of video information and allow access to many simultaneous video streams thus enhancing retrieval and analysis of video clips by multiple operators.

A rarely discussed issue is the utilization of a central database. Many manufacturers produce recorders with a database included. Though fine for a site with single unit, a site that has two or more units will need two or more databases, i.e. 1 per unit.

The utilization of a central database means that all recorders can be configured from a single computer where it is possible to run a report or get status, event or configuration information from every unit in the system from a single computer. It means that the management of events can be accomplished from a single location including the archiving of multiple recorders back to a single archive server. Thus a single database reduces management complexity, increases usability and therefore reduces the overall cost of ownership.

With all the recent advances in DVR technology, there still seems to be a problem with the integration of CCTV technology and that of Access Control. Access Control manufacturers are still producing their products with an RS232 port to send ASCII commands to the CCTV system and the CCTV manufacturers are merely plodding along producing an array of digital VCR replacements. No one yet is producing a single holistic solution or integrating the two technologies.

Consider the benefits if there were to be a single platform that would allow programming, control and monitoring of both the Access Control and CCTV system from a single screen. The cost savings of such a system that eliminates the duplication of servers and workstations would be considerable.

Analyzing historical data utilizing two discreet systems can be cumbersome even though they are interfaced. Clocks on two separate PCs may drift out of synchronization, making retrieval of data difficult and frustrating over time.

True integration will provide the ability to attach video clips to alarms and events on a single workstation, thus an operator should be able to click on an alarm and launch the video clip of the event that caused that alarm. Using a single database on a single server means that the times of the alarm occurrence and video clip will always be in sync.

Currently there are manufacturers launching Digital Video Servers that are capable of running other applications, such as Digital Video, Access Control, ID Management, Guard Tour, etc. which lowers the cost of ownership even further.

It is clear to more and more people, that embracing digital CCTV is a wise choice. However, the choice of technology is about what works best for you in your particular circumstances and within your budget rather than have inappropriate and possibly expensive technology forced upon you.

When speaking with a consultant, ask questions and explain your circumstances and concerns and allow them to aid you in choosing equipment that is best for you. You should never feel you were forced or tricked into buying a system that is inappropriate.

Special thanks to Phil Mailes of Lenel Systems; UK