What is Variable Bit Rate (VBR)? (Explained)

What is Variable Bit Rate (VBR)?

Variable Bit Rate, or VBR, signifies the specific type of encoding used for online video and audio streaming and digital data to adapt the rate of compression more dynamically depending on the changes in the contents of the files.

In simple words, VBR, refers to the term used in the fields of both computing and telecommunications and signifies the bit rate used for encoding video or audio.

Based on the data type, in VBR, the bit rate is altered constantly while encoding.

KEY TAKEAWAYS

• Variable Bit Rate encoding is a process in which the rate of output data transfer is always adjusted based on the density of the data slice.
• VBR defines the final bit rate of the file as an average of the bit rates of other files.
• There are different types of VBR encoding each with diverse features and functionalities.
• Variable Bit Rate encoding generates a video stream of higher quality.
• VBR is most suitable for uploading Video On Demand (VOD) without affecting its quality negatively.

Understanding Variable Bit Rate (VBR)

Variable Bit Rate, or VBR, refers to the method where data is transferred at a flexible rate.

It is actually an encoding process where data segments are packed according to their complexity.

This ensures that the transmission of data is optimized to produce high-quality streaming.

According to the ATM Forum, VBR refers to the Asynchronous Transfer Mode (ATM) quality of service type. It defines two specific types of rates, such as:

• The real-time Variable Bit Rate (rtVBR) and
• The non-real-time Variable Bit Rate (nrtVBR).

Moreover, in addition to the traffic specifications, it also involves two other types of cell rates such as:

• Peak Cell Rate (PCR) and
• Sustainable Cell Rate (SCR).

Using VBR will help you to:

• Attain a much higher bit rate
• Transmit large files

Though VBR is good to use for on-demand video transcoding, it may not work quite as well when used for live streams because it takes quite a long time to process the required data.

Variable Bit Rate can be of different types. Each of these types are somewhat different from one another. These are:

• Quality VBR – This technique uses a single-pass encoding process to encode the data.
• Unconstrained VBR – In this technique, a multi-pass encoding technique is followed to encode the data.
• Constrained VBR – In this particular type of VBR technique, once again, a multi-pass encoding process is used to encode the data.

In VBR encoding, the file size setting is normally based on multi-pass encoding.

This specific process permits the user to stipulate a specific size for the target file, and it happens in two specific stages, such as:

• In the initial pass, the encoder usually evaluates the input file and calculates the likely range of bit rates automatically. It also evaluates the average bit rate.
• And, in the final pass, the same encoder allocates the existing bits among the whole video. This typically helps in achieving the desired uniform quality of the video.

Should You Use Variable Bit Rate Encoding?

Yes, you should use Variable Bit Rate encoding if you are specifically focused on achieving better results and higher-quality VOD streaming.

However, in order to use it, you should make sure that it is compatible with your video player and other video encoding hardware and software.

This is important because VBR is a relatively new technology and is typically not compatible with anything and everything thrown at it.

Typically, Variable Bit Rate encoding has varied uses mainly due to two specific reasons. These are:

• The VBR files allow varying the amount of output data in each of the time segments.
• The process also allows for a higher bitrate and, therefore, a larger storage space that can be assigned to the more complex sections of the media files and less of them to the less complicated ones.

It is the average of these different bit rates that is used to evaluate the average bit rate for the VBR-encoded file.

Is Variable Bit Rate Lossless?

To put it in the simplest way, if you consider MP3 specifically, then you can say that Variable Bit Rate is lossy. On the contrary, FLAC is lossless. As for others, you can consider VBR to be lossless.

However, you will need to look into it a bit more deeply to have a better understanding.

Typically, the term ‘variable’ in VBR signifies that it allows saving space when you encode a video or audio file.

This, in turn, signifies that there may be a few specific segments of the track that are of better quality as compared to the other parts of it.

Therefore, there is a chance of losing information while a file is being compressed, as it is in the case with the MP3 files.

This means that the ‘lossless’ aspect is itself variable. It regulates the number of bit rates required at different points in time by the analog audio for converting it into digital format and for ensuring that the quality of it is not lost.

That is why there is a difference in the bit rates in each individual section.

Therefore, it can be said that, just like Constant Bit Rate, Variable Bit Rate also does not have anything to do with whether the codec is lossless or not.

In fact, the thing that is particularly important in this case is whether the bit rate of the data fluctuates or does it remain the same all through the period and its entire length.

Is Variable Bit Rate Good?

Yes, Variable Bit Rate is quite good to use for on-demand video uploading since it offers a much better quality-to-space ratio as compared to other forms of encoding for the same type and amount of data.

The bits available for use are much more flexible, which helps in encoding data much more precisely, whether it is video data or audio data.

Another significant aspect of the Variable Bit Rate encoding is that it uses fewer numbers of bits in less demanding passages and more bits for those passages that are much more difficult to encode in order to produce better results.

What Does a Variable Bit Rate Do?

Variable Bit Rate actually offers a much better control technique while you are into video or audio encoding. It helps in achieving better video and audio streams with respect to the file size ratio.

The best aspect of it is that it helps in changing the bit rate continuously according to the complexity of the media during the process of encoding.

Usually, the working principle of Variable Bit Rate involves using a specific VBR algorithm.

This algorithm ensures that there is a proper balance maintained between the quality of encoding the data and the rate of compression of the files.

This eventually helps in creating a file which is much smaller in size, but is of superior quality.

VBR Vs CBR

• As far as audio-only streaming or live audio broadcast is concerned, the Variable Bit Rate method falls a bit behind the Constant Bit Rate process.
• If you consider the popularity of the two methods historically, Variable Bit Rate is a bit less popular in comparison to Constant Bit Rate encoding technique.
• Though the Variable Bit Rate method does not affect the quality of video negatively and produces high-quality streams, it is not as widely compatible or supported as the Constant Bit Rate method of encoding.
• Variable Bit Rate encoding technique is most suitable for VOD or Video On-Demand transcoding without any time limitations, but Constant Bit Rate process is ideal for live stream encoding and multimedia encoding.
• The quality offered by the Variable Bit Rate encoding process is usually better but is variable, but in Constant Bit Rate technique it is more consistent, but not optimized.
• The speed of Variable Bit Rate encoding is a bit slower in comparison to Constant Bit Rate encoding.

Questions & Answers:

Conclusion

As you can see after reading this article, Variable Bit Rate plays a very important role in enhancing and maintaining the quality of online video streaming.

It is quite capable and reliable enough to meet all your specific streaming needs, depending on the type of video content, and yield high-quality results and viewing pleasure.