How To Choose The Right DVR
December 1st, 2008
A DVR is basically a computer with the sole purpose of capturing images and electronically communicating with existing security devices. Having the right knowledge and understanding of Digital Video Recorders will help you make the best purchasing decision. In many cases, price does not always reflect performance.
One of the most, if not the most, important specification for you to consider is the record resolution. The record resolution is the amount of vertical and horizontal pixels captured for each channel during record. Most DVRs have record resolutions ranging from QCIF to 4CIF (also referred to as D1).
QCIF: 176 x 120 pixels
CIF: 360 x 240 pixels
2CIF: 704 x 240 pixels
4CIF/ D1: 704 x 480 pixels
Mostly all DVR systems playback in full D1 resolution. So if you are recording at anything lower than this resolution, it is impossible for you to truly playback at D1 resolution. In other words, if a DVR is recording each channel in CIF, it will not be as good quality as if it were recording in full D1. Casinos and airports are two common examples where D1 is required per channel. The important thing to remember here is that the RECORD specification is much more important than display specification. So for example a16 channel DVR advertised as 480/120FPS display/ record means that it is only capable of recording a maximum frame rate of 120FPS or 7.5 FPS per channel and simply “displays” at 480FPS.
The next important specification for you to pay attention to is the compression. H.264 is the latest technology and usually the most expensive, but worth every penny. Video quality is superior with H.264 and harddisk space usage is minimal compared to the competing technologies. H.264 has become today’s standard of video encoding and will continue to be in the future. Most advertised DVRs neglect to tell you the brands of processors used so make sure to inquire carefully and keep in mind that Motorola, Texas Instruments, and Philips are the current market leaders in H.264 hardware DSP processors.
It is also very highly recommended that you stick to DVRs that are DSP based because the ones that aren’t; aren’t PC compliant. In other words, something as simple as replacing or upgrading your harddrive can become a nightmare because you need to get new firmware from the manufacturer which can sometimes take months or sometimes simply impossible to get. ASIC or non DSP based DVR systems are less expensive, but long term, they are likely to become obsolete.
Is there a difference between FPS and fps? Yes, they are the same exact letters, but they actually represent two different things which are very important to take notice of. FPS stands for Frames Per Second and the standard for Real-Time is 30FPS… same as used in Hollywood films and H.264 DVRs. In the MJPEG and JPEG2000 environment, fps translates to FIELDS per second. An odd and an even field is required to make a frame in JPEG/JPEG2000 DVR so always remember to divide the JPEG20000 advertised FPS specification in two in order to get an accurate comparison of actual frame rates you are purchasing.
DVR systems vary greatly when it comes to features, performance, and flexibility. Most of the time these are things that are dependent on the processor used in your DVR. Let’s take for example the ability to do remote internet monitoring… this is a feature that is very handy because it allows you to always have access and control of your surveillance camera system even when you are away. So what makes one DVR better than the other when it comes to remote internet monitoring? Well let’s take MJPEG and JPEG2000 DVR systems… they are both capable of remote internet marketing, but because of their huge file sizes, the frame rates can be extremely slow. On the other hand, H.264 DVR systems display video online about 6 times faster than MJPEG/ JPEG2000 systems. H.264 DVR systems also feature control over bandwidth, VOIP, synced audio capability, and remote PC recording and monitoring.