What is vbr bitrate?

One of the most common encoding parameters available for live and on-demand streaming is bitrate control, which dictates how the encoder allocates the encoded audio and video data within the file. There are a variety of methods available for controlling bitrate, two of the most common being constant bitrate (CBR) and variable bitrate (VBR). True to their names, CBR refers to encoding a stream at a single set bitrate, whereas VBR refers to encoding or transcoding stream segments at different bitrates according to their complexity. In this article, we’ll take a closer look at both of these methods and when to use them.

Historically, CBR has been the standard for streaming. Most digital broadcast streams are encoded using CBR, because the streams are transmitted through fixed bandwidth connections with a low tolerance for stream variations.  Broadcast professionals migrating to streaming production tend to prefer CBR because they’re used to it. Similarly, CBR was strictly adhered to when, during the early years of streaming, producers attempted to deliver video to 28.8kbps modem connections.

The average video download speed in the U.S. today is over 90 Mbps, with 4G and 5G dominating mobile connections. As such, the bandwidth variations caused by VBR typically won’t interrupt last-mile playback. As you’ll read, however, there are still very good reasons to use CBR for live productions.

First, let’s take a closer look at how these technologies work and what distinguishes them.

CBR stands for constant bitrate. If bitrate refers to the amount of data transferred over a set time, then a constant bitrate is a consistent stream of data at a set speed. This makes it highly reliable in that you can choose a set bitrate and know what you’re getting. However, it is not responsive to the size or complexity of the data being transmitted. This less nuanced approach could lead to lower overall quality, depending on your target bitrate and streaming goals.

All of that being said, CBR is the more popular of the two methods given how widely supported it is. In particular, it’s helpful in situations that require real-time encoding, like live streaming. It’s also a better option for multimedia encoding, but we’ll get more into these details later. If you choose to encode at a constant bitrate, the rule of thumb is to choose a higher bitrate to ensure a quality stream. Just know that you may need other steps in your workflow, like the help of a streaming solution, to further adapt your stream to end-user devices.

Pros

Cons

VBR stands for variable bitrate. If CBR refers to a stream with a single static bitrate, then VBR refers to a stream that involves multiple bitrates applied to different segments of a single stream. This works by encoding data segments at different bitrates according to their complexity. Of course, the real answer is a bit more complicated, as there are multiple VBR subtypes that work in slightly different ways.

To understand these differences, you first need to understand single-pass versus multi-pass encoding (sometimes called VBR 1 pass vs. VBR 2 pass when referring exclusively to VBR). Single-pass encoding is exactly as it sounds — the data is encoded on the fly a single time. This is how CBR works for the stream as a whole. VBR can do this as well for various data segments.

Multi-pass encoding is only used by VBR and involves taking an average bitrate from the various encoded data segments and either using that to encode all of the segments or to determine a range for encoding all of the segments. This creates some consistency in how the segments are encoded but with more nuance than straight CBR.

Pros

Cons

Let’s use the Adobe Media Encoder interface to further illustrate the differences between these two encoding methods.

As shown in the below screenshot, CBR assigns a single data rate to the file and encodes in a single pass. As the name suggests, the encoder maintains a constant bitrate over the duration of the file, which doesn’t vary by the complexity or motion in the video.

In contrast, with variable bitrate encoding, the encoder varies the bitrate allocation over the file according to encoding complexity, stealing bits from easy-to-encode scenes to apply to hard-to-encode scenes so they look better. In operation, as shown below, you assign both a target bitrate and a maximum bitrate, with some encoders also allowing you to set a minimum bitrate. You’re essentially telling the encoder to average 2 Mbps over the duration of the video file, but in no cases let the video bitrate exceed 4 Mbps.

This 4 Mbps is the “constraint” in constrained VBR (as discussed above). In practice, almost all VBR is constrained VBR, because you always want to set some bandwidth limits to ensure smooth streaming. You would call the configuration in the below screenshot 200% VBR, because you’re instructing the encoder not to exceed 200% of the target bitrate.

With these terms defined, let’s see how the Adobe Media Encoder did in meeting our targets, using the files we just encoded as viewed in a free tool named Bitrate Viewer. Note that this test file has seven seconds of easy-to-encode low motion followed by seven seconds of hard-to-encode high motion. The first of the following two screenshots is the CBR stream, the second the VBR stream. Bitrate Viewer is in seconds view and the dark blue blocks show the data rates for each second of video. The faint blue line is the average bitrate over the file.

On the upper right of each image, you see the average bitrate for each file: 2029 kpbs for the CBR file and 2019 kpbs for the VBR file. So, the Adobe Media Encoder hit the target bitrate for both files. This reinforces the point that the VBR and CBR decision doesn’t impact total bitrate, just how the bits are allocated throughout the file.

You can also see the peak bitrate is 3,373 for CBR and 5,360 for VBR, indicating that the bitrate wasn’t perfectly constant for the CBR file, and that the encoder missed the maximum constraint for the for the VBR file. This is typical for desktop encoders like Adobe Media Encoder (as opposed to live streaming encoders), where hitting these targets is seldom relevant.  In contrast, most streaming encoders offer closer adherence to the target and maximum bitrates.

That said, you can see that the average bitrate is much more consistent in the CBR stream than in the VBR stream. The CBR stream allocated most of the bits evenly over the entire file, the VBR stream allocated much more of the bits to the hard-to-encode region at the end of the file.

With these two patterns in mind, ask yourself two questions:

Finally, while it may not be evident in our experiment, CBR infrequently produces transient drops when the encoder sacrifices short-term quality to meet the target bitrates. This is one reason why some producers may avoid CBR despite its widespread support and popularity.

By now the strengths and weaknesses of each of these methods should be fairly clear. CBR is faster, more consistent, and less dynamic. VBR takes longer, but its variable nature makes it more adaptable and better able to produce a high-quality stream. So how do you choose? Let’s break it down by the two most common streaming use cases.

Though one-pass VBR encoding is possible, VBR is most effective when the encoder can scan the entire file and identify the hard-to-encode and easy-to-encode regions. Obviously, two-pass encoding isn’t available for live encoding, which usually makes CBR the better option.

Additionally, when encoding onsite and then streaming to the cloud for transcoding and packaging, producers often work with tight outbound bandwidth constraints. In these instances, you want very tight control over your outbound bitrate, because data rate spikes could exceed available bandwidth and stop the outbound stream.

Most producers prefer CBR for cloud transcoding of live streams because it keeps outbound bandwidth requirements relatively consistent. Remember that all viewers of a live stream watch the same bits at the same time. If you’re serving thousands of viewers simultaneously, and the bitrate spiked by 200%, then you could temporarily exceed the capabilities of your delivery ecosystem. In contrast, even if thousands of viewers were watching a VOD asset simultaneously, they wouldn’t be watching the same sections, so the effect of the variations would even out.

Recognize that encoders don’t produce total flatlines when delivering CBR video. Apple’s HLS Authoring Specifications state that for “live/linear content, the measured peak bit rate MUST be less than 125% of the BANDWIDTH attribute.” This is good advice whether you’re distributing via HLS or DASH.

Constrained VBR (CVBR) is preferred for video-on-demand (VOD) because it delivers better overall quality than CBR and avoids transient quality issues sometimes experienced with CBR. The constraint applied should vary by geographic region and the connection speed of your target viewer.

In terms of region, if your viewers are typically in the U.S., Europe, or the Asia Pacific, the speed of desktop, living room, and mobile connections are all very high, and unlikely to be exceeded by data rate swings in a CVBR encoded file delivered via VOD. On the other hand, if your typical viewer is watching over 3G or you’re targeting countries with much slower connection speeds, tightly constrained VBR is appropriate.

Referring back to the Apple HLS Authoring Specifications, Apple recommends “for VOD content, the peak bitrate SHOULD be no more than 200% of the average bitrate,” or 200% constrained VBR. If you’re distributing VOD to viewers watching on relatively high bitrate connections, then this is good advice for both HLS and DASH encoding. For countries with lower bitrate connections, use 110% constrained VBR, which would limit maximum bandwidth to 110% of the target.

The same general rules apply for audio-only streaming: use CBR for live and consider VBR for audio on demand. That said, although virtually every video encoder enables CBR and VBR configuration options for video, relatively few offer the same option for audio.

If audio is an important component of the streaming experience, as with concerts, ballets, operas, and similar performances, it’s worth experimenting with VBR audio to optimize the on-demand experience. For most other content, going with CBR for live and on-demand is probably the simplest option.

The following Wowza Video encoder settings are generally recommended. However, note that what works best for your video stream will depend on your use case. Additionally, your camera or source encoder may contain encoding restrictions that could affect these recommendations.

Frame Rate

Keyframe Interval

Audio Bitrate

Video Bitrate

Still not sure which bitrate methodology or encoding best practices would best suit your needs? Learn more about Wowza Video and Wowza Streaming Engine or contact one of our experts for guidance.*

Broadcasters have a lot of choices when it comes to configuring their encoder settings. The settings they choose will determine the quality of their streams. There are two main types of encoding that broadcasters can choose from constant bitrate (CBR) and variable bitrate (VBR) encoding.  It is important to be able to compare VBR vs CBR.

In this post, we’re going to provide an in-depth comparison of CBR vs. VBR. We will also introduce a third option, which is constrained VBR. After we provide some background on each of these technologies, we will identify which is best in different streaming scenarios. To wrap things up, we will review some other related encoder settings. You will know what is CBR and VBR are.

Bitrate measures the amount of data that is transferred over a period of time. In online video streaming, video bitrate is measured in kilobits per second, or kbps. Bitrate affects the quality of a video. Streaming with a higher bitrate helps you produce higher-quality streams.

When it comes to online video streaming, broadcasters often make their content available in multiple bitrates. This is referred to as multi-bitrate streaming. This allows viewers to access the bitrate that is appropriate for their internet speed which allows them to access the highest quality content with the least amount of lagging, skipping, and buffering.

Adaptive bitrate video players have been game-changing since they automatically deliver the rendition of the video with the appropriate bitrate in response to a real-time analysis of each viewer’s internet speed.

Bitrate is also something that is important in the encoding or transcoding stage of the streaming process since this too deals with the transfer of data.  As we mentioned, constant bitrate streaming (CBR) and variable bitrate streaming (VBR) are the two most popular types of encoding, which is why you often see VBR vs CBR comparisons.

Constant bitrate, which is commonly abbreviated as “CBR,” refers to transmitting data at a constant rate. For encoding, this refers to an encoder outputting data at a constant rate. It is not responsive to the size or complexity of the files that it processes. The variables don’t matter with a constant bit rate; the output remains constant.

CBR is preferred in many streaming situations because it has been the standard in online video streaming for some time. Since it is so popular in the live streaming industry, constant bitrate is the most compatible option.

Since CBR uses a constant transmission, the bitrate is set at a single rate and measured as such. It’s recommended that you set your bitrate relatively high so that your encoder can handle more complex segments of data as it processes your video. CBR video encoding works best when you set it up right.

The consistency of CBR makes it well-suited for situations where video content must be encoded in real-time. CBR is not suited for storing data. For real-time live streaming, CBR is a great solution.

Variable bitrate, which is commonly abbreviated as “VBR,” refers to data being transmitted at a variable rate. With VBR encoding, segments of data are packaged by their complexity so that the transmission is optimized. Encoding in VBR makes it possible to process at a higher bitrate and transmit larger files.

In terms of encoding, data is output at a set rate per time segment, and variable bitrate is measured by taking the average bitrate of the entire file.

The fluctuating aspect of this method of encoding makes VBR best suited for on-demand video transcoding. This is because it can take longer to process the data. VBR streaming works well with on-demand video, but not as well with live streams.

There are a few types of VBR that are slightly different from one another called average bitrate, quality variable bitrate, unconstrained variable bitrate, and constrained variable bitrate. Constrained variable bitrate is the most notable of these four.

It is also important to point out that VBR is not as widely supported as CBR.

Constrained variable bitrate, or constrained VBR, is another bitrate control setting that is less commonly discussed but growing in popularity.

Constrained VBR is a type of VBR encoding that requires setting a maximum bitrate and a maximum buffer window. Constrained VBR uses two encoding passes to process data. With VBR 1 pass vs 2 pass, you end up with a higher quality video.

Here is a quick overview of constant bit rate vs variable bit rate, so you can see the top features and differences between these two encoding methods.

With constant bit rate vs variable bit rate video, CBR is best for live streaming encoding, and VBR is best for on-demand videos.

Before we dive into the use cases of VBR and CBR, it is important to acknowledge the similarities and differences between encoding and transcoding.

Encoding refers to converting a video from one format to another. In the context of live streaming, this refers to converting the RAW video files that are captured by the camera into a digital format that is able to be streamed over the internet. This is important because RAW video files are too bulky to be streamed.

Encoding is made possible with dedicated encoding hardware or software.

Transcoding refers to compressing video files to create copies in different sizes. These copies are called “renditions.” Transcoding is generally used for on-demand video streaming. Many online video platforms, including Dacast, are equipped with cloud transcoding tools that transcode video files as they are uploaded to the platform.

CBR and VBR are both important in video and audio encoding. Neither is better than the other since they both serve unique purposes due to their individual strengths and weaknesses.

Let’s break down the use cases for these two encoding processes.

CBR is the best setting for live stream encoding. The consistency of CBR makes it more reliable for time-sensitive data transport. This is ideal for live streaming since most live videos are broadcasted at a single bitrate.

Since constant bitrate processes data at a consistent rate, there is no concern of the bitrate exceeding internet speeds. However, the reliability of this method leads to sacrificing quality in some situations.

It is possible to use VBR for live stream encoding, however, it is rarely recommended unless it is using a one-pass setup.

Constrained VBR is the optimal setting for on-demand video transcoding because it is capable of handling larger files while still maintaining some sense of consistency. Overall, VBR produces better quality streams, and on-demand video transcoding provides the flexibility to use VBR, so it’s a no-brainer.

Variable bitrate produces higher quality streams. Since there is less time sensitivity in transcoding on-demand video files, you don’t have to worry about the bitrate exceeding internet speed which gives you the flexibility to lean into the benefits of VBR.

Just like video content, audio-only streaming should use CBR for live audio broadcasts and VBR for on-demand audio streaming.

However, some audio-specific encoders will not give you the option to choose. In that case, you must go with whatever option is available to you. Audio files are much less bulky than video files, so either option should be fine. If possible though, go with CBR audio for live broadcasts. VBR quality is great for on-demand audio streaming.

Dacast recommends using CBR for live broadcasting on our streaming platform. That’s because the constant bitrate is more reliable for encoding video content in real-time.

There are some other encoder settings that we require for our live streaming software. Straying from this configuration may cause issues in your stream.

Here are our required settings:

Please note that these settings are specifically for live streaming. Please check out our transcoding walkthrough for more relevant information on configuring your transcoding settings on Dacast.

In addition to the live streaming encoder settings we mentioned above, broadcasters must choose resolution and bitrate settings to achieve their desired stream quality.

There are different bitrate and resolution combinations required to create streams in ultra-low definition, low definition, standard definition, high definition, and full high definition.

Here is a breakdown of the resolution and bitrate settings for achieving each video quality:

CBR and VBR play different roles in online video streaming. It is important to use the appropriate option for your specific streaming needs. In the debate between CBR vs VBR for your video, it depends on your type of content.

The bottom line is that CBR is more consistent and reliable for time-sensitive encoding, and VBR produces higher-quality results. CBR is the best option for live streaming, whereas constrained VBR is the best option for on-demand video upload.

Now that you have a better idea of how CBR and VBR compare, it is time to put this knowledge to work. If you are new to live streaming, we recommend taking advantage of Dacast’s 14-day free trial. You can use OBS Studio, which is a free, open-source encoding software, to familiarize yourself with the technological functions we’ve described in this post.

All you have to do to access your free trial and start streaming is create a Dacast account, and you’ll be up and running in no time. No credit card or binding contracts are required.

GET STARTED FOR FREE

The term variable bitrate (VBR) refers to a bitrate control technique, and it is commonly used in sound or video encoding.

VBR is used to achieve improved video and audio quality in comparison to file size ratio. Depending on the complexity of the media the bit rate is continuously changed during the encoding process.

As opposed to constant bitrate (CBR), VBR files vary the amount of output data per time segment. VBR allows data to be transferred at a higher bitrate, with more storage space for more complex media segments and less space for less complex media segments.

Although VBR encoding requires more processing time than CBR, for most video content it produces superior visual quality

Bitrate is the number of bits that are processed when sending files, and the transfer rate of the data that makes up a media signal. It is normally measured in seconds. For video, this is typically measured in megabits per second (or Mbps, or Mb/s); with audio, it is usually is measured in kilobits per second (or kb/s or kbps).

The term bitrate, also written as bit rate, gets tossed around a lot in mobile development, so it might be good to go over some common terminology:

Variable bitrate (VBR) is the recommended bitrate used in sound or video encoding. Unlike constant bitrate (CBR), VBR files vary based on the amount of output data in a given media segment. CBR encoding control maintains a set bitrate over the entire video clip.

With VBR, the average transfer rates may be calculated to determine the average bitrate for a file.

Whenever you encode a video file for streaming distribution, you need to choose a bitrate with a bitrate control technique.

The issue with using CBR is that since the same bitrate is applied to the entire file it often limits the potential image quality, particularly for more complex video. CBR delivers lower overall quality than VBR. And it introduces the potential for dramatic transient quality issues.

The advantage of VBR is that it produces a better quality-to-space ratio compared to a CBR file of the same data. The bits available are used more flexibly to encode the data more accurately.

The primary disadvantage is that, as mentioned above, VBR may take more time to encode. In the past, some players could not decode variable bitrate files properly, but the vast majority of players support it. As VBR encoding algorithms have improved, most of the problems have been resolved.

When encoding video you have a choice of which bitrate and bitrate control technique you are going to use.

Unless there is a specific reason for using CBR, we recommend that you choose VBR.

VBR produces significantly higher quality at similar bitrates. The primary benefit of VBR encoding is that it allocates a higher bitrate to the more complex segments of media files and lower bitrates to the simple segments.

The primary downside of VBR encoding is that it requires more processing time, but the superior visual quality should more than make up for the extra effort.

Constant bitrate (CBR) encoding is typically not the best choice for streaming. Encoding video with CBR comes at the expense of quality, because it requires the compression engine to assign bits to content based on time rather than by image or sequence complexity.

Occasionally, compression requirements mandate that you use CBR. One example might be live event video streaming. Another example is satellite television broadcasts, in which many channels are multiplexed into one transport stream that has limited bandwidth.

Bitrate measures the amount of data that is transferred over a period of time. In online video streaming, video bitrate is measured in kilobits per second, or kbps. Bitrate affects the quality of a video. Streaming with a higher bitrate helps you produce higher-quality streams.

There are three options in YoloBox: constant bitrate encoding (CBR), variable bitrate encoding (VBR), and constant quality (CQ). This blog defines the terms and provides recommendations for when to use all three.

The acronym CBR stands for Constant Bitrate. If you are streaming video or audio using CBR encoding, the data required to provide that service is set at a constant data rate.

CBR is preferred in many streaming situations because it has been the standard in online video streaming for some time. Since it is so popular in the live streaming industry, constant bitrate is the most compatible option.

The consistency of CBR makes it well-suited for situations where video content must be encoded in real-time. CBR is not suited for storing data.

The abbreviation VBR stands for variable bitrate. The term itself suggests its functionality. All you have to do is realize the difference between the terms ‘constant’ and ‘variable.’ In other words, regular bitrate and variable bitrate are concepts with exactly opposite meanings.

In terms of encoding, data is output at a set rate per time segment, and variable bitrate is measured by taking the average bitrate of the entire file. The fluctuating aspect of this method of encoding makes VBR best suited for on-demand video transcoding. This is because it can take longer to process the data.

Constant Quality aims at achieving a fixed visual quality. While ensuring the highest compression rate in a single encoding, each frame is allocated enough bits to achieve the required visual quality.

We recommend using CBR for live broadcasting with YoloBox and YoloBox Pro. That’s because the constant bitrate is more reliable for encoding video content in real-time. CBR also produces higher-quality streams than VBR, making them ideal for large audiences that consume live content online like sports games or concerts.

CBR and VBR play different roles in online video streaming. It is important to use the appropriate option for your specific streaming needs. The bottom line is that CBR is more consistent and reliable for time-sensitive encoding, and VBR produces higher-quality results. CBR is the best option for live streaming, whereas constrained VBR is the best option for on-demand video upload.

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