When considering a surveillance system for your home or business, the selection of the digital video recorder (DVR) will be the most important component of the entire security camera package. The first choice you will be faced with is do you want a standalone DVR, or a PC based DVR? There are advantages and disadvantages to both. The PC based DVR is a DVR that uses software normally stored on a hard drive and either a windows or lynux based operating system. The main reason one should choose a PC based DVR is that they are compatible with various intelligent surveillance softwares such as facial identification, license plate recognition, missing item detection etc... The downside to PC based DVRs are that they are generally less reliable, more vulnerable to viruses and hackers, and should the hard drive fail, it could result in the loss of not just the stored video, but possibly the entire software package.

 

A standalone DVR was designed for a single purpose. Standalone DVRs differ from PC based DVRs because they use embedded hardware for compression and operation. If the hard drive should fail, the worst that could happen would be the loss of stored video. The operating system of a DVR is stored in the hardware, not on the hard drives. Also, because standalone DVRs cannot be windows based they are far less vulnerable to viruses and hackers. In general standalone DVRs also offer the benefit of being less expensive. The drawback to the standalone DVR is the fact that it cannot operate in conjunction with other specialized software such as the PC based DVR.

 

When selecting the right DVR there are many factors to consider. First, depending on the application you will be using it for, you will want to decided what resolution you want to record in, and what frame rate (basically refers to the number of pictures per second the unit is able to record in) you want. Almost all DVRs will display live video in the highest resolution (720x480) and in real time (30 frames per second). More important though, is at what resolution and frame rate can the unit record in. Don't be fooled by the term realtime DVRs. There are 2 different resolutions and frame rates with every unit. The live video display, and the recording resolution and frame rate. The key here is you want to closely examine the recording resolution and frame rate. The recorded footage is what you will have to refer back to if an event should occur. The quality of your video evidence will depend on the resolution and the frame rate. Recording resolution is usually refered to as either a variant of CIF (360x240) or D1 (720x480) . Currently, D1 (720x480) is the highest resoltion that a standalone DVR can record in. In most cases, a standalone DVR is not able to record in D1 (720x480) in realtime (30fps) on all channels at the same time.Typically, the higher the resolution you choose to record in, the lower the frame rate you will have to select. 

 

Look for the following specification under "recording speed" or "frame rate" when comparing DVRs. The highest recording speed for a 4 channel is 120fps, for an 8 channel is 240fps, and a 16 channel is 480fps. Compression is the next factor to consider. Earlier DVRs used less compression. JPEG 2000 was very common. Less compression does provide better quality video, but less compression also takes up much more storage space. A unit using H.264 compression will require far, far less storage space than a unit using MJPEG 2000 compression or even MPEG4. Compression is a means for reducing the size of the file containing the recorded video for storage. Typically, compression is done by analizing each frame of video and discarding all but the most useful portions of the image. Basically, it discards everything that is the same from frame to frame and retains the changes. Currently, the most effecient form of compression is H.264. This offers up to 40% more use of your storage than MPEG4 compression.