When evaluating digital platforms, there are many factors that need to be identified. Figuring out real time recording versus time-lapse recording in digital terms along with defining resolution, calculating storage and everything in-between proves to be an ongoing challenge for most. The objective of security management has always been to capture as much quality information as possible using the least amount of recording media. This holds true in digital as well. From the beginning of video in security applications, the standard of measuring real time for all moving images was defined at 30 frames or 60 fields per second.
In today’s world, everything is an acronym. Unfortunately, when selecting and evaluating digital systems there are variations in terminology since different manufacturers use different words. For example, with regard to how much information will be recorded, you will most often find references to ips (images per second) and fps (frames per second, or fields per second). The question you need to ask is if fps stands for “frames per second” or “fields per second?” Or does IPS equate to field or frames? A rate of 30 frames per second is equal to 60 fields or images per second, which is true real-time NTSC video. Some manufactures record at 30 ips while other manufacturers record at 60 ips. Although this seems confusing at first, there are specific differences between the two and should be clarified during the selection process.
What about compression?The next thing to consider is the compression technology the manufacturer is utilizing. For example, H.263, Wavelet, MPEG-2, MPEG-4, JPEG and MJPEG are a few compression modes you will most often see – each of which offers specific benefits as well as sacrifices. The selection of compression technology for your system needs can vary greatly.
Compression affects both bandwidth and resolution. Some compression methods or hybrid versions are better at passing high quality images at lower bit rates. Some compression technologies are better suited for streaming live video over LANs or WANs. It is somewhat argumentative as to which technology is better suited for recording digital video in security applications. Those questions can be answered through an understanding of one’s intent for their system. Determining the most important factor for your facility will help you decide the most appropriate compression technology for your needs.
Most of the accepted enterprise-level DVR solutions utilize MPEG-2 or MPEG-4 compression and portray resolution as CIF (Common Intermediate Format) or SIF (Source Input Format). A variation of CIF or SIF seems to be the most regularly used. CIF/SIF images are 352 pixels wide and 240 pixels tall.
QCIF is one-quarter CIF and too low a resolution in my opinion to be considered for security applications of any type. CIF is just a tad better resolution than what a VCR produces, and in most cases adequate for back-of-house operations and parking. 4CIF uses 704x480 pixels resolution or 640x480 pixels, roughly four times the area of CIF. This loosely equates to DVD-quality video. This will produce the highest quality images available in today’s marketplace. If budget permits, then by all means go for it. D1 is a newer term being used which produces 720x480 for NTSC and for product evaluation purposes, is comparable to 4CIF. 2CIF varies from product to product but is usually 640x240 pixels, although I have recently seen it defined as 340x480.
If asked where I find the most problems and confusions, the answer would definitely be storage. Storage calculations unfortunately are not the exact science they should be. When calculating storage, stress that it is calculated at 100-percent motion for budget purposes. Manufactures try to stay competitive and storage is the most expensive part of the system. When putting out your request for proposal, be sure to include how many days you will be retaining your video. For example: “system to record 512 cameras at 4CIF RAID5 for no less than seven days.” Buy the system per your parameters. Forget how many Terabytes you are buying. In your contract or proposal, make sure it clearly spells out your desired storage retention so you are covered should it be under-specified.
Although DVRs have come down drastically in price, digital recording is still quite an expensive investment. Be sure to choose a qualified systems integrator who is teamed with a reputable manufacturer. Request demonstrations, then ask to demo the product at your site for a week or two if possible.