Digital Video Recorder Buyers Guide

What is a Digital Video Recorder?

A Digital Video Recorder (DVR) is simply a computer hard drive with functionality and connections that are designed for the CCTV Security market.

What are the advantages of a DVR?

Before DVRs existed the most common way of recording CCTV video footage was through a multiplexer and timelapse VCRs. However, DVRs have many advantages over the multiplexer and VCR:

• DVRs can have a huge storage capacity and so eliminate the need to frequently change tapes.
• DVRs don?t have problems with tape or VCR?s wearing out and so consistently produce higher quality recorded images.
• Because DVRs record digitally, you can retrieve recorded footage instantly rather than scanning through hours of video tape.
• Some DVRs have motion detection software built-in, removing the need for separate PIRs.
• Some DVRs can be viewed over a network or the internet allowing them to be used for remote viewing.
• DVRs often work out cheaper than the combined price of a time-lapse VCR, video tapes and a multiplexer.

What should you look for in a DVR?

The number of cameras

DVRs can record 1, 4, 8, 9, or 16 cameras at a time.

How long will a DVR record for?

Everybody has different recording needs and many factors affect how long a DVR will record for including: the number of cameras, the compression technology, the frame rate, the picture quality, the picture size, and the amount of recording time required. To make it easy for you we have created a DVR calculator that will tell you how long a DVR will record for.

What is the maximum frame rate of a DVR?

All DVRs have a maximum frame rate. This simply refers to the maximum number of frames that a DVR can record in one second at any one time. For example: a four camera DVR with a maximum frame rate of 50 frames per second (fps) can record at up to 50fps. If all four cameras are set to their maximum recording rate this will achieve (50/4) 12.5fps per camera. Television is displayed at approximately 25 fps.

The frame rate that is right for you depends on your needs. For example if you are just counting bodies then 1fps will be plenty. On the other hand if you wish to catch people stealing small items from a shop then 6fps will normally be enough.

More advanced DVRs will automatically increase the fps rate on a camera where motion has been detected, providing more footage on an event.

What is the compression method used?

DVRs use various compression methods for compressing video footage. This reduces the amount of hard drive space that is used. Additionally, if a DVR can be viewed over the network or the internet a sophisticated compression method reduces the amount of data that needs to be transmitted. TeleEye DVR?s have a unique patented encryption technology that compresses video footage to the extent that the TeleEye system still works well over a normal telephone line.

Compression methods include Wavelet, MPEG, and MJPEG.

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