RECORDING TIME
A typical DVR has 4, 8 or 16 individual camera inputs also known as channel inputs that allow the DVR to record video. The video information is stored using a hard drive similar to the one in your computer. This video information can be recalled by time, date or events such as motion. The size of the hard drive is determined by the amount of time you wish to record (in days). There are several factors that change the required hard drive size such as frames per second, compression, quality and resolution.
Frames Per Second
When choosing your DVR the most common question is how much time can I record. This is a very tricky question that we will try to explain. First part of the question we need to consider is FPS (frames per second) sometimes also referred as IPS (Images per second). The faster or more fluid recording movement the more hard drive space is required. Looking below at the simulation you will notice first lion is moving at a respectable pace. This first lion will consume a hard drive much faster then the third lion.
DVRs are purchased by their frames per second 60, 120, and 240. This number represents the entire DVR capability which means the frames per second are divided by the number of cameras the DVR can record.
Example: a 16 camera DVR that can record 120 frames per second will actually record each channel at
(120 / 16 = 7.5fps) similar to the second lion above.
Compression
Compression is the technology used to save video on a hard drive. There are several type of compression available but our DVRs use JPEG, MPEG and H.264. Compression is an algorithm of mathematics used to make each picture in the video smaller in size on the hard drive without loosing the quality of the picture. As we know you can't get something for nothing so every compression type comes with a price of quality.
Over the generations of DVR technology the video quality gets better and the size gets smaller. JPEG is an old format that is still used in several DVR brands including our GVR models because of its price point. MPEG compression has recently become very popular because the price has come down to the residential market and the quality rivals a standard DVD players available in most homes. H.264 is the newest and probably the best format available because of its speed, quality and now with the cost of overseas chips is at a price point of MPEG compression.
Below you will see a simulation of the three different formats.
Quality
This is the last DVR option that will effect the storage necessary on the hard drive. Quality usually has 4 levels including low, medium, fine and superfine. The quality option is similar to compression in that the image and size is effected, however, although quality may be adjusted for any compression, it is most noticible in better images. Example, if you choose low quality using a JPEG image, the recorded image will be VERY poor. This is why quality is more affected by better images as in MPEG and H.264. Look below for a simulation of the quality options.
| H.264 Compression |
| Superfine |
Fine |
Medium |
Low |
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Resolution
If all the above was not enough there is one more factor to the problem. That factor is resolution or more commonly thought of as picture size. There are usually three sizes available 360x240, 720x240 and 720x480. These represent the horizontal and vertical dots that it takes to make each image in the video. As you might assume, the higher the resolution the better the quality the more room necessary needed on the hard drive.
Summary
Wow, what a lot of information. The good news is there are calculators that can compute this information into time which tells what hard drive you should buy. However, you will still need to make some decisions, like any calculator you still need to enter information before you can get an answer. So you need to review the above headings and choose what is important for your needs. Quality vs record time vs budget.
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