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Difference between CBR (fixed), VBR (variable) and ABR (average) [bit rate]

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Difference between CBR (fixed), VBR (variable) and ABR (average) [bit rate]

constant vs variable bit rate

CBR (constant bit rate)
VBR (variable bit rate)
ABR (average bit rate)
There are three types.

I will present the differences between them.

See the following article for the “bit rate”.

Reference: What is a bit rate? Relationship between image quality and sound quality [Video / Audio]
Related: Difference Between VFR (Variable) and CFR (Fixed) [Frame Rate]

Every feature
I will briefly explain each feature.

CBR (constant bit rate)
CBR (constant bit rate) is

A video with a constant video bit rate.

for instance,

Scenes with intense movement
Scenes with complex audio
Even in “scenes that require a large number of bit rates”, for example, the bit rate to be assigned is constant and

Motionless scene
Scene without audio
Even in “scenes that do not require a lot of bit rate”, the bit rate to be assigned is constant.

In this way, a video that assigns a constant bitrate to “Assign a constant bitrate!” In any scene it is called CBR (constant bit rate) video.

The following are the characteristics of CBR.

(○) Search (fast forward / rewind) is fast
Since the transfer rate is the same, you can search instantly.
(○) File size can be predicted
If you decide beforehand to “encode at XX bit rate”, you can predict the file size from resolution, frame rate, video length, codec, and so on.
(○) Easy to use as a material
In the case of video, there is no need to worry so much, but in the case of the sound source, various problems can occur such as drift of sound with VBR or ABR (so if there is a possibility that it will be used later to video edit material, etc. Better to encode with CBR)
(○) Fast encoding speed
It doesn’t change much, but unlike VBR and ABR, you don’t need to “predict” it, so encoding is faster.
(X) Image quality and sound quality are not very good for the file size
Even a monotonous scene that does not require a lot of bit rate allocation may be assigned a certain number, or a scene that requires a large bit rate may not have enough bit rate, so the image quality and sound quality for the file size. Cospa is bad
VBR (variable bit rate)
VBR (variable bit rate) is

A video whose bit rate varies depending on the scene.

VBR_figure

for instance,

Scenes with intense movement
Scenes with complex audio
In “scenes that require many bit rates”, such as assigning many bit rates and

Motionless scene
Scene without audio
For “scenes that do not require a lot of bit rate”, assign a lower bit rate.

In this way, a video that assigns only the required bitrate according to the scene, “You need this bitrate, don’t you?” It’s called VBR (Variable Bit Rate) video.

The following are the characteristics of VBR.

(○) Image quality (sound quality) by file size is the best
Compared to CBR and ABR, the image quality (sound quality) by file size is the best.
(△) Unpredictable file size after encoding
The file size cannot be predicted because the bit rate fluctuates extremely depending on the content of the material to be encoded. (However with the x264 encoder etc it is possible to predict because it puts an upper limit on the file size and allocates the maximum bit rate within that range)
(X) Old MP3 players may not play well
If you have an old MP3 player, the playing time display may be strange, the bit rate display may be strange, or you may not be able to play from beginning to end.
(X) When used as video editing material, it may cause sound drift.
For more information, see the following article
Reference: Causes and countermeasures for sound deviation [Encoding]
If you want to encode video with high image quality and low capacity, VBR is your choice.

By the way, in VBR, it is common to determine video quality by “quality standard” (CRF value in x264 encoder) rather than by “bit rate standard”.

For example, instead of saying “Encode at 192bps!”, Specify something like “Encode at

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What is a bit rate?

Audio Bit rate

The bit rate in a video is “how much information is packed in one second”.

BIT RATE

What if the bit rate is high?
Basically, the higher the bit rate, the better the picture and sound quality.

* Although it is closely related to the “codec” described later, it will basically improve.

There are two types of bit rates
Bit rates are assigned separately for “video” and “audio”.

The higher the bit rate assigned to “video”, the better the “image quality”.
The higher the bit rate assigned to “voice”, the better the “sound quality”.
Also, the sum of the two bit rates is “is called the oval bit rate (total bit rate)”. (This oval bit rate is called “video bit rate”)

▲ If you open the video file properties and open the “Details” tab, you can see “What is the bit rate?”

(However, this Windows function is unreliable, so it is better to use video analysis software like MediaInfo)

soon,

Oval bit rate = video bit rate + audio bit rate
It becomes the calculation formula.

So even if it says “bit rate is high!”, It may mean “video bit rate is high” and “audio bit rate is not high”.

In other words, in such a case, the video will be “Image quality is good, but sound quality is not good …”.

Basically, the file size of “audio” is much smaller than that of “video”, so even if you increase the bitrate of “audio” significantly, the overall size of the file will not change as much.

Therefore, “speech” is often encoded uncompressed (linear PCM).

Relationship to image quality
The higher the “video” bit rate, the more accurate the color information that can be assigned to all pixels.

as a result

High bit rates improve image quality and
If the bit rate is low, the image quality will deteriorate.

▲ High bit rate (12 Mbps, 2.57 MB) ▲ Low bit rate (90 kbps, 20 KB)
* Actually, it is a gif video, so the bitrate is not accurate.

Bit rate difference

Also, in the case of a low bitrate, if you allocate bits evenly to all pixels, you will run out of bits, so in scenes where similar colors are continuous (such as a scene where the blue sky stretches without end), etc. Try to reduce the bits preferably.

As a result, “block noise” ↓ is likely to occur in such scenes.

Block noise
▲ Example of block noise (block noise)

Relationship to sound quality
The audio bit rate is

Sampling rate (Hz) x bit depth (bit) = bit rate (bps)
It can be expressed by the formula.

For example, when recording sound as digital data

How often do you record (= sample rate)
How much data is stored per interval (= bit depth)
Decide and register.

for instance,

Sampling frequency: 44000 Hz
Bit depth: 24 bit
If so, the sound is divided and recorded 44,000 times per second, and the sound is recorded using 24 bits for every 44,000 times.

In other words, if you want to improve the sound quality, you can increase the “sample rate” or “bit depth”.

Increase the sample rate → Soft sound
Increase the bit depth → Increase the expressiveness of the sound, such as finesse and volume
Reference: Meaning and Relationship of Sample Rate, Bit Depth, and Bit Rate

Relationship to codec
I mentioned earlier that “the higher the bit rate, the better the image quality and sound quality”, but the image quality and sound quality are “codecs”. they are closely related to the “.

A “codec” is something like a “compression algorithm” for compressing “video” and “audio”.

Reference: What is video format? Codec difference

for example, “the H.264 video codec” It is a very famous codec that is also used on Youtube and Nico Nico Douga,

(Addendum: Not used now …)

“H.265” which improved the “image quality by file size” from “H.264” There is a codec called “which.

“H.265” is “H.264 at about half the bit rate of”, “H.264 will get the equivalent of image quality and”. (The compression rate is double)

for instance,

Using “2Mbps” video bit rate with “H.264 codec”
Video using “2Mbps” bit rate with “H.265” codec
If there are two videos, the image quality of “H.265” is twice as beautiful even though the bit rate (file size) is the same.

MP3 bitrate types

MP3 bitrate types

Mp3 Bitrate

Bit rate

bitrate

CBR stands for constant bit rate, that is, a constant bit rate that is set by the user and does not change when the part is encoded. Therefore, every second of the part corresponds to the same number of bits of encoded data (even when encoding silence).

VBR stands for variable bit rate, that is, a variable bit rate or variable bit rate that the encoder program dynamically changes during encoding based on the saturation of the audio material being encoded and the encoding quality set by the user (for example, silence is encoded with the minimum bit rate). The downside to this encoding method is that VBR considers the quietest snippets to be “negligible” audio information, so it turns out that if you listen too loud, these snippets will be of poor quality, while CBR makes quiet and loud snippets with the same bit rate …

ABR stands for Average Bit Rate, that is, Average Bit Rate, which is a hybrid of VBR and CBR: the user sets the bit rate in kbit / s and the program varies it, constantly adjusting it to the specified bit. Velocity. Therefore, the codec will be careful to use the maximum and minimum possible bitrate values, as it runs the risk of not conforming to the bitrate specified by the user. This is a clear disadvantage of this method, as it affects the quality of the output file, which will be slightly better than using CBR, but worse than using VBR (with the same file size).

MP3 codecs

The type of programs required to convert file formats. The most common MP3 codecs are:

mp3PRO-codec (uses SBR frequency transform).
LAME codec
fraunhofer-codec

What is the video and audio bit rate?

What is the video and audio bit rate?

Bit Rate

Do you like video production or do you value high quality in movies? You’ve probably come across something like bitrate. It always accompanies the technical characteristics of video recordings and its value determines the quality of the image in the file. When working with converters, you will come across this feature more than once, so it is advisable to fully understand what it is responsible for and how it affects the final product: a video or an audio file.

bitrate

To find out what bit rate is, it is worth understanding how video information transmission works. Any video is a rotating sequence of images. In order not to have a “slideshow feel”, the image change speed must be at least 24 frames / sec. Each box has parameters: width and height. The higher they are, the more pixels are placed in an image, the higher the quality.

Each “point” that makes up a frame has a weight and is equal to 1 byte. Let’s take a Full HD picture and calculate its weight – about two megabytes will be released (1920 x 1080 = 2073 600). So one second of video, containing 24 frames, would weigh 48MB. This is where the concept of bitrate comes in: it is the power to compress a video.

Those. the required file, being encoded, loses weight. But due to strong compression, it may also lose quality. Of course, in reality, not everything is so simple; Much depends on the codec used for encoding. This is the name of the direct compression method. So videos in different formats, but with the same bitrate, can produce images of different quality. The concept of “audio bit rate”, denoting the strength of compression, is also applicable, but for an audio stream.

Bit rate types
Delving into the topic, it is worth noting that the bitrate is not always the same. And now we are not talking about a quantitative indicator, but about a division into types. To work competently with media conversion, read about three types of bitrate: constant, variable, and average, which is a hybrid of the first two.

Constant Bit Rate (CBR)
As the name implies, this type of bit rate does not change during file playback. This compression method allows you to fairly accurately determine the size of the output file and ensure consistent quality throughout your listening or viewing session. But in the entertainment industry, constant bitrate is rarely used due to the impossibility of adjusting it. for dynamic playback, because the files get bigger than they could be.

Variable Bit Rate (VBR)
This type of bit rate is flexible and resistant to change, as a result of which it can be adjusted to the playback object and produce an optimal size / quality indicator. For example, for pictures or musical pieces with a reduced information density, the bit rate will decrease, thus reducing the weight of the object.

Average bit rate
This view is a compromise between the previous ones. The problem with variable bitrate is that changes are automated, and sometimes overcompression can occur. Average bitrate allows the user to set the range in which compression variation will occur. True, the technique of its use is not so simple and is mainly used in professional studios when working on serious projects. An additional advantage of the average bitrate is that it allows you to more accurately calculate the file weight even when the compression force changes.

Explanation of the sample rate, bit depth and bit rate

Explanation of the sample rate, bit depth and bit rate

Bit Depth

This is what happens when you compress audio files
High-resolution streaming and audio promise us particularly good lossless sound when playing digital music. But what exactly does that mean? Sample rate, bit depth, and bit rate are explained.

16-bit 44.1 kHz – CD Quality: This slogan is often used when marketing high-resolution and lossless audio formats and equipment. But what exactly is it about?

israelburrows | Israelsaepblog

The quality of digital audio signals is primarily determined by three things: sample rate, bit depth, and bit rate.

In principle, you have to imagine that a digital audio signal is not a constant flow of information. Rather, music is divided into very, many small “slices” (samples), each of which carries the information for the digital-to-analog converter in a short section.

The more samples a signal has per unit time, the more precisely the original analog signal can be mapped.

The sample rate reveals how tight the samples are: the 44.1 kHz of a CD represents 44,100 samples per second.

Bit depth

Bit depth (resolution) is specified in “bits” and indicates how many different values each sample can assume. With 16 bits (CD quality), this is 2 ^ 16, that is, 65,536. The recording studio usually works with 24 or even 32 bits.

This is where many high-resolution formats come into play that also promise studio quality at 32-bit resolution.

▶ ︎ MP3, FLAC, ALAC, WAV – the most important music formats in comparison

Bit rate

The bit rate (bandwidth) of an audio file in uncompressed formats is initially nothing more than the summary of the sample rate, the bit depth and the number of channels. It is specified in kBit / s and therefore provides an initial characteristic value for evaluating the quality of a file.

Example: A stereo CD stores two tracks at 44.1 kHz with a bit depth of 16 bits. This means that its bit rate is 44.1 kHz x 16 bits x 2 channels = 1411.2 kBit / s