Our Man in the Field: The Process of the IP Solution, Part VIII

Our man in the field explains the basics behind DVRs and NVRs and looks at digital storage essentials


In the last installment of our column (see The Process of the IP Solution, Part VII) we defined the idea of real-time video. It also pulled us into the new intricacies of digital recording. Ah yes, there are options to be discussed here.

In the olden days, we worried about how many hours to record on a 2 or 3 hour cassette. It was a little thing called "time loss factors". You could take the recording speed and divide it by 120 to calculate the number of frames recorded each second. Then you used that to determine how many images you recorded from each camera per second or minute or week. The only other concern was whether or not to alarm the recorder or the multiplexer or both. Alarming the recorder increased the speed of the tape, but had no affect on the switcher so you would end up with more images per camera, but the same amount of time loss while switching between them. Alarming the switcher would lock onto a single camera or flip between two.

So, if the action left the area of the alarmed switcher channel, you lost everything. We had worries. We worried about how many cameras we were switching through when recording. We worried about time loss factors, but, for all intents and purposes, that was about all the options we had to worry about. Today the ball is in a different court, and yet we still worry. Today our worries are:

  1. How much space do we have to store our images and data on?
  2. How do we calculate the amount of space that we need?
  3. How many images per camera do we need or want and under what circumstances?
  4. What level of resolution do we record each camera:
    a. As a group?
    b. Individually?
    c. Under normal circumstances as opposed to duress or alarm?
  5. What format do we store our images in?
  6. Do we want or require off-site monitoring, playback, control, and search capabilities?
  7. Do we require watermarks or encryption?
  8. Do we need or have the ability to download images in a court-accepted format for evidence?
  9. What is a court-accepted format?
  10. Is the format or the unit that we choose for our recording and storage going to be obsolete in five minutes ... and if so, will the company that sold it or produced it still be in business to support updates or upgrades?
  11. Is the software compatible with the other items in my system that have special design and/or needs?

Overall, I could probably come up with 10 or 15 more questions to ask, but I am not here to depress you all or to remind you about how little we all know about our new futuristic recording traps.

The first important question in the equation is storage space. We have to ask how much is required. This is still a maddening experience for me personally. OK, I know it's just math, and math is my forte, right? Right! However, the number of answers required to calculate storage space can be huge. You'll need answers to questions, but you may or may not be able to answer these questions precisely at the time you are trying to calculate your space. Expect questions like:

  1. How many images per camera per second do you intend to record, and, for that matter, how many cameras do you intend to have in your system that are recorded?
  2. How many events will you have in a day, week, month and at what frame rate and for how long each?
  3. What resolution will you require under normal recording circumstances?
  4. If a green car is traveling east on Highway 44 at 65 mph and a red car is traveling west on Highway 44 at 85 mph, at what point will they crash and burn?

OK, you won't have to answer that last question, but the point is that for some of these questions, you may find that you need to make a decision on a potentially expensive and extremely important aspect of your system design in a "half guess" manner. So let me explain and then you decide.

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