Video Bitrate
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Bit rate types
There are three types of bitrate:
Constant (CBR)
Variable (VBR)
Average (ABR)
Let us consider each of them in detail.
Constant bit rate
As the name suggests, constant bitrate is an encoding method in which the value of the bitrate remains unchanged throughout the file.
By setting a constant bit rate, you can quite accurately calculate how much video you will take on a disc.
For example: if the video bit rate is 6,000 kbps, then one minute of video at this bit rate will take 360,000 kbps (6,000 x 60 seconds), which in turn equals 351.5 megabits (360,000 divided by 1024) or 43.9 megabytes. (351.5 megabits divided by 8).
Next, you need to calculate how much space will be needed to store one minute of sound. For example: 192 kbps x 60 s. = 1.41 megabytes.
Therefore, the total volume of one minute of video and audio will occupy approximately 45 megabytes. By multiplying this value by the number of minutes, you get the size of your video file.
The above calculations are generally used for the reverse process, when you need to calculate the maximum allowable bitrate for your video.
Example: there is an hour and a half of video that must be burned onto a DVD disc. Do we need to calculate what bit rate the video should have to get the highest possible quality and still fit on a DVD disc?
You can calculate the maximum bit rate manually or, to avoid bothering with math calculations, use a special program, for example “Bit rate calculator”.
This program is free, requires no installation, and works on any Windows (I personally verified it on Windows 7 and Windows XP). Where to download the bitrate calculator, as well as how to configure and use the program, you can read the article “Bitrate calculator”.
Variable bit rate
Variable bit rate is an encoding method where the flow of information is not constant, but changes depending on how demanding the video is with the bit rate in a given section.
If you have read the article “Compress Video”, then you know that the less the new frame differs from the old one, the less is spent recording it. The conclusion follows from this: the more dynamic there is in the scene, the more is spent recording it, which means that the bitrate value for dynamic video should be higher.
Let’s take two videos as an example.
In the first video, a person sits at a desk in a room and gives an interview. The shooting is done with a tripod. In the frame, except for the movements of the person, nothing changes.
The second video shows a soccer game. There are several footballers in the frame at the same time, who are moving quite fast, + the ball, + in the context of a live mass of fans who are actively “getting sick”.
What do you think, for which video, the bit rate should be higher?
The answer is obvious. For the first video, an average bit rate, or even less, will suffice. For the second, it is desirable to give the maximum, unless, of course, you want a good image quality.
By understanding the above, you will agree that it is impossible to accurately predict the optimal amount of information that will be required to record high-quality video. Everything is further complicated by the fact that even in a football movie there can be scenes that are not very dynamic, for which a low bitrate is sufficient. And in general, in almost any movie, the dynamics change constantly and chaotically.
Naturally, the question arises: what to do? How to choose the optimal video bitrate?
Optimal bit rate
Well, first of all, the most rational thing is to use a variable bit rate, in which the program increases or decreases the data flow, depending on the dynamics of the scene and other factors.
Second, once you’ve set the bitrate value, you need to take one of the most dynamic scenes in the movie and render a small piece of it. After viewing this snippet, you need to visually assess the quality of the resulting video. If it suits her, she will do it in other scenes. If the quality of the scene is noticeably damaged, you should consider increasing the bit rate.
Average bit rate
Average bitrate is a type of variable bitrate that allows you to set a specific (average) bitrate value that the codec adheres to. In other words, it is a hybrid of constant and variable bitrate.
By using the average bit rate, you allow the program to vary the value of the bit rate at its discretion, but at the same time, its average value must correspond to the specified setting.
In most cases, the averaged bit rate is used, as this allows you to achieve optimal video quality, while calculating the final size
