BEYOND VCRs: Video storage and retrieval options in a digital age
Jun 1, 2001 12:00 PM
By CHARLIE R. PIERCE
Find the event by the date, day, hour, minute, second, frame or field. Find it fast and find it now. Review the image at any speed!
For the past couple of years, when it came to digital recorders and storage systems, I have been screaming: Buyer beware. I have not changed my opinion about these systems, but I am starting to yield a little bit. Slowly but surely we are starting to see changes and advancements that are making some sense. Applications are opening up and the technology is becoming more stable ¡ª keyword being more stable. Let's start by listing some options and functions and go on from there.
First, we have all the standards options of a regular video recorder; record, play, fast forward (FF), rewind, pause. This is important to know because lots of folks are really worried that they are not advanced enough to operate a digital recording system. Pure nonsense, but a very real paranoia just the same. Although these are simple functions to which we have become accustomed over the past 30 years, they are, for the most part, names that are now attached to non-existent technology. Because we have gone or are going digital, there may not even be any moving parts associated with the functions that they represent. So rewind, fast forward, play, and pause become moot points.
To make it really easy, let's do a step-by-step comparison between analog video recording and digital recording.
STEP 1: Analog video tape. Task: Convert the incoming video signal, from the camera, into radio frequencies (RF). This is the point in the process where we first lose video resolution. Because we are trying to record so much information on such a small medium (video tape), we must drop something to make the image take up less room. So we first drop the video signal because RF takes up a whole lot less room than the video signal. The net result, however, is a drop in resolution because of the drop in frequency between the two mediums.
STEP 1: Digital recording. Task: Convert the incoming video signal, from the camera, into digital information. We must start out by converting our frequency-based video signal into the electronic Morse code of digital. Just as in standard recording (RF), we must drop something to make the new digital video image fit into a small space. It is the first point in the process where we start to lose resolution. We will compress the image. For the sake of explanation, we will take something that fits into a 4-inch by 4-inch square and we will make it fit into a 1-inch square. We will do this by removing every third pixel or every odd pixel or every odd line of pixels ¡ actually there is no standard of compression within the CCTV industry, so everyone will do it their own way.
STEP 2: Analog video tape. Task: Lay the converted RF information down in magnetic paths on a magnetic-based tape. In the beginning there were no standards here. Some of the old timers will remember that the tape that they recorded on their machine would not play back on their neighbor's machine. The key difference in the security world was between RCA recorders and everyone else. Today, a standard has been established, and everyone uses the same standard in video head technology. Those that had RCA machines had to carry their machines to court for quite a few years before RCA converted to the more popular video head.
STEP 2: Digital recording. Task: Burn the converted, compressed digital information into short-term memory for future transfer onto a magnetic or laser based medium. Magnetic media: floppy disk, hard drive, wire, etc. Laser media: CD, DVD and/or a host of other such options. Again, the key worry is how much space do you have and how you use it. Digital encoded images require as much space to store information as their analog counterparts, at least in this early stage of design. Consequently, the key is not how much space you have to store the information, but how much information can you transfer and still be viable to your application.
You already gave up 15 percent to 45 percent of your resolution (depending on the style of compression used in your digital conversion). The next thing that the majority of digital recorder designers and manufacturers will have you believe is that you don't need as many pictures stored as you are accustomed to ¡ so let's drop every other one or all the odd ones or all the images with pictures of Elvis in them. Comes down to a bit of magic, doesn't it? I realize that little of the visual information recorded is necessary or needed at a given time. However, how do you determine in advance which images are necessary and which ones are not? I have been reviewing and commenting on evidence tapes for 20-plus years, and I have yet to find a tape where someone could have said: "Hey, let's just record the five pictures that happen at 12:01:018875 AM to catch the guy that is going to knock the door down." It's not that easy.
Granted, through proper alarm trigger and/or trap integration, we can narrow the amount of "useless" visual information recorded to a minimum, but to say we only need certain frames is ludicrous. However, there is a group of people trying to sell you a digital recording or storage unit based upon this very possibility.
STEP 3: Analog video tape. Task: Play back and review the recorded information. Simple: put in the appropriate video tape, push rewind, hit play. Advance through the tape by: 1) watching in fast forward mode; or 2) blindly searching in fast forward to the exact spot that you want to review, plus or minus a few minutes; or 3) moving to the next alarm code. Bottom line, retrieval of visual information from a video tape is limited and awkward to say the least. In many cases, you are forced to review the video tape on or through the same equipment that recorded it.
Multiplexers are a fine example of this. Because, over the past 15 years, our industry has yet to set a standard on multiplexer codes, we are still required in most cases to supply a multiplexer to the court or whomever to review the visual evidence on our video tape. The second half of this bad scenario is that when using a multiplexer or switcher to review the information, it must be done at the same speed or a slower speed than it was originally recorded.
STEP 3: Digital recording. Task: The strongest and most important option that digital recording and/or storage systems offer is their ability to sort and retrieve visual information. It can be done within minutes or seconds from 10 or more criteria specifications. Find the event by the date, day, hour, minute, second, frame or field. Find it fast and find it now. Review the image at any speed! The key here is that the language is no longer necessary. What are we fast-forwarding or pausing or rewinding? We don't move through digital information in the same fashion. The computer knows exactly where an image is stored. It only requires a single, quick scan of its memory bank.
However, the amount of visual information you have stored, the compression rate and the format will determine how long the scanning process takes. This is another reason that many manufacturers are in a hurry to compress your information without regard to the needs of the application. They want to keep the storage space that is needed to be scanned to a dull roar. More scanned area requires more memory in the main computer area ¡ more memory means more cost to produce ¡ more cost is more expense to the consumer. If it is more expensive to the consumer, he is less likely to buy in a progressively aggressive market.
STEP 4: Analog video tape. Task: Prepare a copy of the recorded information for review in another location. This is a simple process of playing the tape in one machine while recording it in another. However, this is also a second point of resolution loss. Whenever a copy of a video tape is made, we can lose up to 25 percent of the original resolution. Bottom line is that the original will always look better than the copy. However, we can play this copy back in any video recorder machine.
STEP 4: Digital recording. Task: Prepare a copy of the recorded information for review in another location. Again a simple process of dumping the data onto a floppy disk, CD, or DVD. Or, you may want to play the information back and make a standard VHS video tape recording. All are viable ways to go. However, if you drop your stuff down to an electronic format, you will be required to have a like machine at the other location in order to play it back. If you decide to use a video tape, you will have resolution loss in the copy and in each generation of copy thereafter.
All right, we have looked at some of the similarities, but what about the differences between analog and digital. Where do we start? How about, are you getting what you paid for? Does it do what you were told it would do? Do you get the programming capabilities that were demonstrated? Can you record camera #1 in the 24 hour mode, while camera #2 takes a single picture every five days, while camera #3 is left to record only during alarms, etc.? Is the resolution of the final playback really as good as it looks or is that one-inch by 1-inch image a mirage? What does it look like if you enlarge the image to a usable size? Are you able to record all of your cameras in real time (30 pictures per second) or will you run out of space within a few seconds? How much space do you have, and how much will your application need? It keeps going and going. Did you really have a demonstration or did someone put on a really good show?
At the end of the day, test the product! Verify that it does what you expect and need it to do!
More importantly, verify that it will do what your application requires of it.
Charlie R. Pierce, president of LRC Electronics, Davenport, Iowa, is a leading authority on CCTV and a regular contributor to Access Control & Security Systems Integration.