Bit rate in DVR. What is it and what does it affect?
When talking about digital video recording, the term bit rate will surely ring a bell. This is an important parameter that affects image quality. Including recording to a DVR.
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If you are intimidated by foreign words, the bit rate can otherwise be called the recording speed or compression ratio. Because that’s exactly what happens: the compression of the video stream. How? Let’s take a look.
After the light strikes the matrix and subsequent digitization of the image, a very dense stream of digital video signal is obtained at the output. Also, the higher the video recording resolution and frame rate, the bulkier this stream will be. You cannot write it directly to a memory card; It will fill up very quickly with huge video files and you may just not be able to cope with such a flow of information. This is why the original video stream is compressed to an acceptable bit rate. This parameter is just the output data rate. Basically it reflects the speed at which the video is written to the memory card.
Bit rate can be calculated in bits, kilobits and megabits per second – (bit / s, bps, b / s), (kbps, kbit / s, kbps) (Mbps, Mbit / s, Mbps). Most of the time, in megabits. The bit rate of the recorded video can be checked on a computer with a video editor or via the file properties menu. By dividing the number by 8, you can determine it roughly in megabytes per second; it will be more convenient to compare it with the speed of your memory card.
The bit rate indicator depends, as you might guess, on the processor and the software and hardware that is properly optimized to process the video stream. If all conditions are met, the video stream will be compressed with high quality and with minimal loss. Otherwise, the video will have noise, blurred images, artifacts, and other nasty distortions.
The bit rate also affects the size of the file. For example, at a relatively low bit rate (less than 10 megabits per second) more clips can fit on the memory card and cheap low speed cards can be used, but the video quality and details will be low. At a higher bit rate (10-20 begabits per second and more), the image will be of higher quality and more detailed. But the file size will also increase, so you need a memory card of the appropriate size and speed (16GB and above, class 10).
Manufacturers rarely indicate the bitrate on the box, therefore it is almost impossible to find out this indicator before buying. However, sometimes on the packaging you can see promises, for example, “8 hours of video in maximum quality at 32 GB”. And in this case, the bit rate can be roughly calculated. The formula is not complicated:
We took 32 gigabytes and, using the school’s computer skills, we converted them to megabits by multiplying them by eight and by 1024. Then we divided the resulting number by the number of seconds in eight hours.
– (32x8x1024) / (8×3600) – We get the result of 9.1 megabits per second.
Let’s clarify that the result will be conditional. First, because the actual volume of any card is always less than indicated. Second, the promises in the box can be just promises. Therefore, before buying, it is better to carefully study the selected model, having learned the speed of writing in the reviews.
So what bit rate should I be aiming for?
Given the adequate quality of the filling of the recorder (matrix + processor + lens + software), according to our practice, let’s say that this figure is in the region of 15 to 45 megabits per second. This bit rate allows you to get a fairly adequate video quality during the day. Again, only during the day, because night recording, as we all know, is still a weak point of many recorders due to insufficient lens aperture and small matrix pixel size.
Note that currently the maximum bit rate for recorders has been reached: 45 megabits per second, but only when working with a card with a capacity of 32 gigabytes or more. Some companies, notably Datakam and BlackVUE, are introducing bit rate selection options in settings. We find this option controversial. In our opinion, all drivers are initially interested in the highest quality videos, and it is easier to set the maximum bit rate for the recorder right away and just choose the right memory card in terms of speed and volume.
