To calculate storage, there are two variables one needs to know: the image size in kiloBytes (kB) and how many images per second are to be recorded.
Since many systems also allow users to turn on and off recording for part of the day, the formula accounts for this as well:
- Image size (kB) x images per second x hours of recording (per day) x 0.0036 = Hard drive per day (GB)
- For example, the calculation for an image size of 6kB at 16 images per second, recording for 24 hours, is: 6kB x 16 x 24 x 0.0036 = 8.29GB per day
- To calculate longer time periods such as a week or a month, simply multiply by the desired number of days. Using the same example, it would be: 8.29GB/day x 30 days = 248.8 GB
Equally important as storage calculation is the issue of what bandwidth is required to achieve quality video transmission – a paramount concern for anyone who plans to use the system remotely because too much required bandwidth leads to slow-moving images. Although different to the storage algorithm, the information one needs to know for bandwidth is identical:
- Size of an individual image in kBs and number of images sent per second.
- With those two numbers, you can convert the kBs (from the images size) into kiloBits per second (kBps) since that is the standard measurement for transmission. To convert kBs to kBps, multiply the number by 10 (it is actually eight bits per byte, plus a start-bit and stop-bit required for transmission).
For example, each 6kB image in the example below would be 60 kBps. When you know how many images per second a digital video recorder can send, you can then calculate the bandwidth requirement with the following formula:
- Images per second x (Image size in kB X 10)
In our example, if we used 20 images per second and an image size of 6kB, the bandwidth requirement would be:
- 20 X (6 X 10) = 1,200 kBps or 1.2 Mbps (mega bits per second)
- Another frequently asked question security technicians receive from their customers is what bandwidth should they expect and how many images per second should they receive over a specific bandwidth. Now that we know our bits and bytes, the answer is simple: divide the bandwidth by the image size in kBps. An example using 768kBps and the same image size would be: 768 / (6 X 10) = 12.8 images per second
- For many digital video recorders, the bandwidth limitation can be set so that the video being transmitted does not affect other traffic on that particular network. Generally speaking, the more often (or longer) a remote site is accessed, the more impact the video has on network traffic and the performance of other programs, such as e-mail.
It is also important to remember that the actual available bandwidth you have to work with is determined by the slowest connection segment between two points. For example, if facility A and B both have high speed LANs, video transmission within the facility will be very easy. If both facilities were connected via a dial-up phone line, transmission between facilities would be very slow. Even high-speed connections to the Internet (which is being used as a transmission medium more frequently these days), can offer different bandwidths.
One of the more popular communication lines nowadays, DSL, comes in two types: ADSL (asynchronous digital subscriber line) and SDSL (synchronous digital subscriber line). While SDSL has the same performance in either direction, ADSL promises a smaller bandwidth “upstream” (from the site to the Internet) and a higher bandwidth “downstream” (from the Internet to the site). The latter is the more common line used for Internet browsing because it usually requires small “upstream” bandwidth for commands (e.g. send me the page www.yahoo.com) and large “downstream” bandwidth (the actual page).
In the case of video transmission applications, it is important to know the type of DSL line installed at the facility you are working in. Usually the transmitting site (DVR) needs the SDSL, while the receiving side (PC) can be ADSL.
Imagine, for example, the ADSL was specified as 768kBps downstream and 128kBps upstream, while the SDSL line was specified at 768kBps both ways. If the ADSL is installed at the transmitting side, the available bandwidth would be only 128kBps (the “upstream” bandwidth) and it would not matter if the receiving side were ADSL or SDSL. If the transmitting side is SDSL, the available bandwidth is 768 kBps and the receiving side could be ADSL or SDSL.
Ultimately, even though network administrators probably know their sites like the back of their hands, they still cannot accurately predict how much bandwidth is available for video transmissions at any given point on time. While the maths is correct, the actual frame rates will vary, especially if the Internet is part of the transmission path.
Real-time recording
From Visimetrics comes the OCTAR Real-Time digital video recorder, which records up to eight channels. It will record all eight cameras simultaneously at 25 frames per second with little increased storage capacity requirement. It has the same familiar user interface as the existing range of OCTAR DVRs and is file compatible with other OCTAR systems. This means that OCTAR Real-Time can be included on the network with other OCTAR DVRs to complement existing CCTV systems.
The end user can review the CCTV footage from any OCTAR at any point on the network; from any playback station, any OCTAR DVR, central control station or standard PC (using playback software). As with all products from the OCTAR range, it maintains compatibility for ease of use and standardised installation.
OCTAR Real-Time has been specifically designed for high security applications where it is critical to capture high frame rate CCTV recordings, such as cash counting, casinos, police interview rooms and detention areas.
Reader Service No 139
Free vouchers
The DTL range of digital recorders from Baxall has been given a facelift. These easy-to-use recorders have been re-cased to fit in with the Baxall product style. And they are now available at a new low price, making them a suitable replacement for VCRs. Also they are now available with a removable hard drive and writeable CD drive.
To celebrate the new design, features and price point, Baxall will reward installers purchasing the recorders with a £10 Kingfisher voucher redeemable at B&Q, MVC, Woolworth’s, Big W and Comet.
The DTL range now consists of 40, 80, 160, 240 and 320GB models, all with or without Ethernet compatibility and audio. The Ethernet versions enable users to directly connect to an existing Ethernet LAN or WAN. Authorised users can then view live or recorded images, save them to view later or distribute them to others, making it highly flexible. All models are easy to use and have been designed to look, feel and operate just like a VCR, but with all the advanced features you would expect from a hard disk recorder. Searches can be conducted using date, time, camera or alarm criteria.
Reader Service No 140
For small applications
The DTS (Digital Triplex System) from Videte is the digital image recording system for small and medium video security applications. The system integrates multiplexer, time-lapse recorder and infrared motion detector functionality in one appliance. DTS Entry Line is a low-cost solution which has been designed specifically for very small applications with up to four cameras.
Entry Line can display and record live images and play back archived images simultaneously. These high-quality digital images are displayed on a monitor, offering users a choice of display options.
The integrated motion detection function enables the connected cameras to make event-driven recordings. An intelligent storage management system determines the storage space required by each individual camera and automatically allocates the appropriate hard disk capacities. In conjunction with high-resolution JPEG compression, this ensures that existing storage capacity is fully utilised.
For DTS Entry Line, the functionality and handling features of a conventional video recorder have been reproduced on a state-of-the-art digital image recording system. The system can be operated intuitively by mouseclick and guarantees maximum ease of use with its patented graphical user interface. Thanks to factory default settings, installation work is kept to a minimum.
Reader Service No 141
Innovative combination
The AurorAcorD from Vicon Industries is an innovative combination of multiplexer and digital/audio recorder which allows 16 channels of video to be recorded to the unit’s hard drive in a variety of settings for recording rate, sensitivity and quality. Recording time is maximised by a Wavelet compression algorithm which condenses video information without compromising quality.
In addition, the audio utilises a similar codec compression scheme to optimise recording times and limit the effective bandwidth to 6KHz.
AurorAcorD can be fitted with one or two hard drives or one hard drive and a CD-R/W drive. The hard drive stores the motion video and audio in a proprietary format along with alarm, time and titling information for each camera.
It features full telemetry control (PTZ). Using front panel keys, it can remotely control up to 16 camera domes/PTZ drives using RS-422/485 protocol. Display options include play back through a VGA monitor.
When our experts Bench Tested it last November, they concluded: “AurorAcorD is an excellent piece of kit, genuinely easy to set up and use, capable of outstanding results and hopefully it will inspire other manufacturers to follow suit.”
Reader Service No 142
Simple replacement for a VCR
Reader Service No 143
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