Digital video recorders (DVR’s) are a great tool for security survelliance in that they offer the incorporation of several products formerly required in a closed circuit television system. The digital video recorder replaces the switching element (switcher, quad, or multiplexer), which allows us to view and record multiple cameras. It is the recorder which replaces the videocassette recorder and allows us to archive video. It can be the server allowing us to view video over our LAN, Wan, or the Internet.

Storing video to a hard drive requires a lot of space, so several compression techniques are utilized which leads to confusion when trying to decipher products specifications. Mpeg, Jpeg, HS 263, Wavelet, etc., etc. Since there is no standardization it can be confusing. Remember the old VHS or Beta controversy when videocassette recorders were introduced? Since there is no standardization as to the compression technique utilized, there is no definitive determination about the amount of video that can be stored on any given size hard drive. Each manufacturer’s machine is different and they will publish a storage capability relative to the size of the drive in the model that you elect to use.

Real time video is 30 frames or 60 fields per second. Normal television is 22 to 24 frames per second. You need to have realistic expectations given the number of cameras and the application especially if it goes over the Internet. There are typically two types, one operates like a personal computer and the other has more limited functions. Using a DVR is relatively simple and most models come with good documentation. Viewing stored video is much faster and easier. One of the true advantages of digital is that you can go directly to any event given the time and date. You do not have to search clumsily through hours of video to review an event. Motion detection, lighting adjustment, camera identification, and a host of other features are standard on most machines. One of the best things about DVRs is no videotape to switch, store, rewind, or operate.