Most Digital Video Recorders (DVRs) are nothing more than a hard drive, a bit of firmware, and an encoder/decoder. What this means is that they are not digital at all. Most DVRs can't even accept a digital signal. Most DVR units use encoders and decoders (usually this is proprietary technology). The encoder compresses analog video signals into a format of digital language. The decoder then converts the outgoing signal back to analog for the monitor(s). In some cases, the DVR may be designed to accept IP or digital signals, but here again there may be a problem of compatibility as there are no set standards for the type of digital output our IP cameras and field encoders use.
To top it off, most of the DVRs use one format or another of proprietary compression for recording. This means that to play a video segment back, off-site, you may end up having to convert the digital signal into a new format such as a .mov file or MJPEG or whatever. The second half of this ugly snake is that you may end up having two or more DVRs at multiple sites that are unable to communicate or playback video information between them. What a waste! It's like having a diesel car at a methane pump. The lesson is that you'll need to pay attention to the details as you assemble your equipment.
Network Video Recorders (NVR) are glorified DVRs. OK, that is a bit of an oversimplification and a little cruel to the manufactures of NVRs, but it's not so far off as to miss the mark completely. NVRs generally have several options that DVRs cannot compete with. The first and most obvious is in the name. NVRs are designed to work over the Internet. Of course, some of you are saying, "My DVR works over the Internet!" and you may be right. However, there is little or no comparison between DVRs and NVRs once they are connected to the Internet.
Most DVRs will transmit a highly compressed image or group of images. Additionally, controlling the DVR from afar may be easily done, but what about controlling the system? NVRs tend to give you full control of the system, right down to individual Pan/Tilt/Zooms. NVRs are designed for large capacity storage (usually) and are generally considered to be "open-ended" technology. Yes, they may have a base recording format that is proprietary, but it is open to outside influences. Newer DVRs carry many different types and quality of features, but in most cases, if you want to beef up the system a bit, you must beef up the DVR. NVRs not only carry many interesting recording and playback features, but they can generally be upgraded via software.
DVRs tend to come in group formation inputs of 4, 8, 12, 13, 16 and/or 24 cameras. Need to add one camera to your existing 16 camera system? Watch out, you may have to purchase another DVR and stack them. That can mean you're paying another $2,000 to $3,000 for one camera. NVRs, on the other hand, are usually open ended. With an NVR system, if you need to add more cameras, you buy an inexpensive encoder and there you go. Overall, the size of your system (the final size); the interactive qualities that you will require between sites and/or for off-site monitoring; and the requirements that you have for "open architecture" design will be what determine if you will use a single DVR (or a stack of them) or if you will break into an NVR-based system.
If you think about it, this kind of sounds like everything else that I have been saying for these past months. Design the application and then investigate, test and apply the equipment to the job ... not the other way around.
OK, so what about all the other questions? Many of them I have answered in past columns. However, I will make you a promise to answer everyone of them next time. From there we will step into compression factors and the net result of recording. After that, it will be time to discuss the differences between on-site surveillance as opposed to off-site monitoring. For some reason, a huge portion of our industry just seems to have problems telling the difference between the two. Once you understand, however, you will never have trouble telling the difference between apples and oranges again. Until then, keep your head down and always think before purchasing or selling equipment ahead of the application's design and/or before a good, on-site, 7-day test. See you when my next column appears in October on SecurityInfoWatch.com.