Category: Audio and video

Bit rate concept

Concept

Bitrate: literally, the transmission rate of information bits. It is common to use the bit rate when measuring the effective information transmission rate through the channel, that is, the “payload” transmission rate (in addition to that, the channel can transmit service information, for example, start and stop symbols for asynchronous transmission or control symbols for redundant coding). The baud rate, which takes into account the total bandwidth of the channel, is measured in baud.

Bit rate is the number of units of information required to store (transmit) one second of a data stream (generally audio and video files). It is generally measured in ‘kbps’, kilobits per second.

The term bit rate is used in two basic meanings
: channel or device characteristic: the maximum number of bits that can be transmitted per unit of time.
– The size of the data stream transmitted in real time (the minimum size of the channel that can pass this stream without delay).
– A special case is the compressed video or audio bit rate.
Bit rate is expressed in bits per second (bit / s, bps), as well as values ​​derived with the prefixes kilo-, mega-, etc.

The term bit rate (along with subjective quality criteria) is often used as a characteristic to evaluate the performance of lossy compression algorithms.

Bitrate characterizes both the density of the information package and its quality. For example, out of two MP3 files compressed with different bit rates, a file with a higher bit rate will have a higher sound quality (close to the original). At the same time, a file of a different format, with the same bit rate, can offer both better and worse sound quality.

On an audio CD, information is losslessly encoded at a constant 1407 kbps bit rate.

The MP3 format allows you to encode audio information with a constant or variable bit rate from 32 to 320 kbps, that is, they provide five times the compression compared to CD.

Bit rate as a characteristic of digital video and audio

In streaming video and audio formats (such as MPEG and MP3) that use lossy compression, the bit rate parameter expresses the degree of compression of the stream and thus determines the size of the channel for which it is compressed data transmission. Most of the time, the audio and video bit rate is measured in kilobits per second (kilobit per second in English – kbps), less often – in megabits per second (for video only).

There are three compression modes for data transmission:

– with a constant bit rate (constant bit rate in English – CBR)
– with a variable bit rate (variable bit rate in English – VBR)
– with an average bit rate (English Average Bit Rate – ABR)

Variable and average bit rate

The codec chooses the required bit rate based on the parameters (the level of the desired quality) and, during the encoded chunk, the bit rate may change. When compressing audio, the desired bit rate is determined based on the psychoacoustic model. ABR is a variation of VBR in which the codec is compressed to a specified average value.

How to Achieve High Quality Videos with Low Bandwidth Part 2

In contrast, a variable bitrate preset a certain level of image quality that is maintained regardless of whether there is movement in the frame or not. The bit rate will change depending on the shooting conditions and the presence of motion.

Dynamic Noise Reduction, as described above, works on the same principle as Variable Bitrate, but with the addition of smart decision-making capabilities based on the presence or absence of motion. This can reduce the bit rate by 50 percent compared to the standard variable bit rate in non-motion scenes.

Priorization
In addition to reducing noise, prioritization can help lower bit rates. By setting priority areas, you adapt the level of compression for different parts of the image. In the image, you can mark several areas, each of which is assigned the parameters of the compression level. A less important area can be configured to use a higher compression rate and therefore a lower bit rate, while important areas can be assigned a lower compression rate to display in more detail.

Take, for example, video surveillance at the entrance of a building. Some parts of the image showing the sky can be considered unimportant for better compression. The area at the entrance of a building can be marked as important and assigned a lower compression ratio to ensure recognition of facial features and other identifying details. Finally, the driveway can be defined as a zone with normal compression.

Reduce costs with dynamic noise cancellation
The combination of noise reduction and image area prioritization produces measurable results. The key advantage of this combination is that you get a significantly lower bit rate without losing image quality. A lower bitrate, in turn, reduces bandwidth and memory usage.

Take, for example, a shopping center with a video surveillance system with 200 surveillance cameras installed throughout the premises inside and outside the facility. Let’s say the mandatory requirement for 1080p HD video surveillance cameras is to record continuously for 12 hours every day, and after the mall closes, they can only record when motion is detected. In this case, to store the video recorded at a rate of 10 frames per second, you will need almost 70 TB, which will allow you to store it for 30 days. The introduction of surveillance cameras that use dynamic noise reduction can save more than 7 TB of required storage capacity. This translates to over $ 10,000 depending on the storage devices used …. Additional savings can also be achieved by adding priorities in certain areas, which will further reduce the bitrate.

Using dynamic noise reduction and priority targeting in small CCTV systems can provide the ability to record video at a higher frame rate for smoother video (when there are moving objects in the video) at the same cost.

Consider, for example, installing a CCTV system in a retail store with 10 CCTV cameras. Using ten indoor 720p HD video cameras, continuously recording for 12 hours every day, and after the store closes, recording when motion is detected, it can store video recorded at a frame rate of 10 frames per second for seven days using the storage device with a capacity of 4 TB. Now let’s look at the same scenario using the dynamic noise reduction method. With Dynamic Noise Reduction, you can stream video at 20 fps and achieve the same storage time using the same 4 TB storage device. You get smoother video movement for the same price.

The ability to reduce bitrate and therefore bandwidth and memory will be even more important as the industry is moving towards the next generation of 4K images. This is characterized by even higher data volumes and therefore higher bandwidth and storage requirements. As a result, a solution that provides high-quality video with the lowest bandwidth and storage requirements will be the most affordable option for customers.

How to Achieve High-Quality Videos with Low Bandwidth

Megapixel surveillance cameras provide their users with more detailed images; however, these capabilities can affect the cost of the entire video surveillance project.

The amount of data that is transported and stored, in this case, increases significantly. Bandwidth requirements and increased capacity required significantly increase the total cost of an IP video surveillance system. The best way to reduce these costs is on the surveillance camera itself, and this can be achieved by reducing the bit rate.

The bit rate can be reduced, in particular, due to noise reduction. Noise is quite a damaging factor that leads to clogging of the encoding process. It leads directly to an increase in the bit rate.

Optimize bitrate to reduce streaming

Classic noise reduction systems are of two types. Spatial noise reduction techniques are applied within the frame to help reduce noise, while temporal noise reduction averages the pixels over multiple frames. These are very effective techniques for still images, but they can cause problems when there is movement. In the event that a temporary noise reduction is applied to a moving image, a ghost image may appear.

By combining spatial and temporal noise reduction with the ability to dynamically adjust them based on lighting levels and the detection of moving objects, we obtain images with low noise, maximum detail and low bit rate. The bit rate can be optimized by adjusting the amount of noise reduction based on the analysis of important moving objects in the surveillance camera’s field of view. When there is no movement, the bit rate is kept to a minimum. If an important object is detected, the bit rate increases, allowing you to capture as much detail as possible. The result is that the bandwidth requirements of the network remain low until something important happens in the frame.

Other ways to reduce the bit rate
For some megapixel surveillance cameras, the bit rate is limited by default. Constant bit rate is often used for this. The constant bit rate is kept at a fixed level. This can result in a constant high bit rate, and setting a low bit rate can result in poor image quality.

Bit rate in DVR. What is it and what does it affect?

In a conversation about digital video recording, the term bit rate will surely ring a bell. This is an important parameter that affects image quality. Including filming on a video recorder.

If you are afraid of foreign words, then the bit rate can be called the recording speed or the compression ratio in another way. Because that’s exactly what happens: the compression of the video stream. How? Let’s take a look.

After the light hits the matrix and the 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 through the file properties menu. By dividing the figure 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 is dependent, as you might guess, on the processor and intelligently optimized hardware and software to process the video stream. If all the conditions are met, the video stream will be compressed with high quality and with minimal loss. Otherwise, the video will contain noise, blurry 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 indicator is in the region of 15-45 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 photography, as we all know, is still a weak point of many recorders due to insufficient lens aperture and small matrix pixel size.

Note that DATAKAM has currently reached the maximum bit rate for recorders: 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 implementing 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 simply choose the right memory card in terms of speed and volume.

And the last thing: they are unlikely to increase the bitrate incessantly on DVRs.