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Video Motion and the DVR

Video motion is described in FPS (Frames per Second), or sometimes referred to as IPS (Images per Second) It really means the same thing.  Real time video (Video that is smooth looking likes your TV) is displayed at 30 FPS.  That means every second you are shown 30 consecutive still Pictures in a row.  It is similar to when you were a kid and drew on the corner of a book and then flipped the pages to see the image move. Camera video works in much the same way.  A lesser quality DVR will record and/or display less that 30 FPS.  The result is jerky looking video that is essentially missing a lot of pictures, so if you don’t want jerky, sticky looking video then you will want 30 FPS Minimum per camera channel.  This becomes somewhat trickier DVR manufacturers sometimes list their FPS as a total number per system recording rate for example an off brand dvrs may say something like this “16-camera DVR 240 FPS recording and display” what this means is that this DVR will record and display video at 15 FPS per camera for 16 cameras.  You can find your numbers by dividing the total FPS that the system is capable of by the number of cameras that the system is capable of using.

 Some manufacturers have different recording and display rates. You can find those rates in the same way. That means that the recorded video, and what you see on the monitor will be different, so be warned.

Example: an 8 camera DVR that has 120 FPS recording and 240 FPS Display. 120/8 = 15 FPS Recording, and 240/8= 30 FPS Display. The customer that purchases a DVR like this, may like how it looks on the screen, but may be disappointed how jerky the recorded video looks when played back.

Camera Resolutions

IP Cameras

IP (Internet Protocol) Cameras can have much higher resolution pictures than analog cameras, but not always. IP Cameras are measured in a megapixel which means millions of pixels per square inch. So a 1.5 MP (1.5 mega pixel) camera will display about 1,500,000. Pixels per square inch and so a 3 MP camera will display about 3,000,000. Pixels per square inch which is double pixels and so double the clarity of the 1.3 MP cameras.

Having a lot more detail in the picture will give you much more clarity, but will also cause two other problems, the first is motion as I mentioned before in the first paragraph real time video is 30 FPS but not many IP Cameras can process high resolution images at that rate so even if the dvrs can, beware the cameras better also be able to do the same. The second is the picture file size will be much larger, and so the hard drives needs to be much larger to accommodate the increased file size than for analog. This will increase the overall cost of the project.

Hard Drive Storage

Your hard drive storage will determine how long you can save video for. Each individual picture or “frame” you record has a file size much like regular digital camera pictures do. These pictures will take up hard drive space to store. If you are recording at 30 frames per second, then you need to have storage for 30 pictures every second. Wow that is a lot of storage. There are several Compression formats out there (MPEG, MPEG4, H.264 ECT...). Compression formats take a large picture file and compress them so they will not take up so much room on the hard drive. While this does help a lot, we are still storing 1800 pictures every minute. And the higher the resolution of the pictures the more space each picture will need.

One option for saving room on your hard drive is motion only recording, where the recording only happens when there is motion in front of the camera.  This sort of recording may not be helpful if camera for example is located where there is a lot of activity, such as a toll booth, or parking lot.  This approach will not help much because the camera will always be seeing motion, as long as there is activity going on, and thus recording most all the time.

Another option and a poor one at that, in my opinion is to decrease the picture quality.  This will give you smaller size picture files, but this defeats the whole purpose of installing a surveillance system doesn’t it.

When in the market place to purchase surveillance equipment most people have not been exposed to the terminology used in our industry.  It can be confusing and can make it hard to compare systems and cameras. I have written this brief summary and description of the standard terms used in our industry and what they mean, to help you better understand the components that are being presented to you.