In the world of video streaming, there are two main types of bitrate technologies: Constant Bitrate (CBR) and Variable Bitrate (VBR). While both methods serve the purpose of delivering high-quality video content, they differ in their approach to compressing and transmitting data. Understanding the difference between CBR and VBR is crucial for choosing the right streaming solution for your needs.
In this article, we'll delve into the pros and cons of each technology and discuss scenarios where one might be better suited than the other.
Table of Contents
- What is bitrate?
- What is constant bitrate (CBR)?
- What is variable bitrate (VBR)?
- What is constant quality (CQ)?
- Constant bitrate (CBR) vs Variable bitrate (VBR): A comprehensive comparison
- When to use CBR vs VBR?
- CBR or VBR for video streaming
- Recommended encoder settings
- Digital Samba: elevating your video conferencing experience with CBR and VBR
What is bitrate?
Simply put, bitrate refers to the amount of data transmitted per second in video streaming and encoding. It's like the flow of water through a pipe – the higher the bitrate, the more data flows, affecting both video quality and file size.
Bitrate is measured in units such as kilobits per second (kbps) or megabits per second (Mbps). Higher bitrates generally mean better video quality but also result in larger file sizes, impacting storage and bandwidth usage.
In video streaming, various quality levels are achieved by adjusting the bitrate. For instance, resolutions like 240p, 360p, 480p, 720p, and 1080p indicate different levels of video quality. Higher resolutions and frame rates require increased bitrates to ensure clear visuals and smooth motion.
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What factors influence bitrate?
Several factors influence bitrate requirements.
- Resolution plays a significant role, as higher resolutions require more data to display detailed images.
- Frame rate is another consideration – a higher frame rate necessitates a higher bit rate for seamless playback.
- Codecs also affect bitrate. Efficient codecs can achieve better compression, reducing bitrate without compromising quality.
What is constant bitrate (CBR)?
Constant bitrate, or CBR, refers to transmitting data through the internet at a constant rate. In the context of video encoding, CBR refers to an encoder outputting data at a constant bitrate, as such, it’s not responsive to the size or complexity of the file it’s processing.
Since encoding CBR uses a constant transmission, the bitrate is set at a single rate and also measured as such. In most cases, video conferencing platforms set their bitrate relatively high so that the encoder can handle more complex content or data being processed.
Moreover, to achieve optimal video quality and avoid buffering issues, streaming services often utilise rate control CBR techniques to regulate the amount of data transmitted per second, ensuring a consistent and high-quality viewing experience for users.
CBR is a popular choice for most streaming situations because it has been a standard in online streaming for a very long time. Since it’s so popular, it’s compatible with most devices.
What is variable bitrate (VBR)?
Variable bitrate encoding, or VBR on the other hand, refers to data being transmitted at a variable rate. With video encoding, the encoder encodes segments and packages the data according to its complexity so that the transmission is optimised making it possible to process at higher bitrate and transmit larger files.
In terms of encoding, data is output at a set rate per time segment, and the variable bitrate is measured by taking the average bitrate of the complex segments and dividing it by the entire file.
The fluctuating nature of VBR makes it well-suited for on-demand video transcoding. This is because it can take longer to process data. However, it’s important to keep in mind that VBR streaming works best with on-demand video but not as well with live streams.
What is constant quality (CQ)?
Constant Quality, or (CQ), is an alternative encoding mode that 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.
To get the best balance between the video quality and file size (get the higher video quality but in a smaller file size), the main video converters or video editors adopted the Constant Quality as the x264 and x265 encoding modes.
However, unlike CBR and VBR where the bitrate is either fixed or varies based on content complexity respectively, CQ aims at maintaining a consistent level of quality across different bitrates. This means that regardless of scene complexity, CQ ensures a consistent viewing experience for the audience.
In CQ mode, the encoder intelligently allocates the bitrate to maintain the specified quality level. When the content contains complex scenes, the encoder allocates higher bitrates to maintain clarity and visual fidelity.
Conversely, simpler scenes receive lower bitrates, reducing the file size while retaining acceptable quality.
Constant bitrate (CBR) or Variable bitrate (VBR): A comprehensive comparison
When it comes to video streaming and encoding, the choice between Constant Bitrate (CBR) and Variable Bitrate (VBR) can significantly impact the quality of your streaming experience.
Both CBR and VBR are widely used encoding techniques, each offering unique features and benefits. To help you make an informed decision, let's delve into a comprehensive comparison of these two methods.
|
Aspect |
Constant bitrate (CBR) |
Variable bitrate (VBR) |
|
Bitrate allocation |
Allocates a fixed bitrate for the entire video. |
Dynamically adjusts the bitrate based on content complexity. |
|
Video quality |
Provides consistent quality throughout the entire stream or call |
Provides higher quality videos for complex scenes and potentially lower quality in simpler scenes. |
|
File size |
Predictable and stable file size. |
Varies based on the scene's complexity. Larger file size for complex scenes and smaller file size for less complex scenes. |
|
Adaptive streaming |
Limited compatibility with adaptive streaming. |
Well-suited for adaptive streaming algorithms ensuring smooth video delivery. |
|
Bandwidth efficiency |
Less efficiency may result in wasted bandwidth |
Optimises bandwidth usage to ensure high-quality video in varying conditions. |
|
Storage efficiency |
Consistent file size can be advantageous for storage management. |
Varying file sizes may pose challenges for content distribution. |
|
Editing flexibility |
Fixed bitrate which allows for easier post-processing and editing of video content. |
A dynamic bitrate may require more careful post-production adjustments. |
|
Ideal for |
Video calls or conferences with stable and limited bandwidth. |
Video conferencing over varying network conditions and changing bandwidth. |
|
Content types |
Best suited for video conferencing with constant scene complexity. |
Ideal for dynamic video conferences with varying content compatibility. |
|
Visual experience |
Potential for compression artefacts in complex scenes |
Enhanced visual experience in high-motion and complex scenes |
|
Encoding efficiency |
Efficient for static and straightforward video content. |
Efficient for video content dynamic or visually complex content |
|
Compatibility with devices |
Well-suited for devices with limited processing capabilities. |
Compatible with a wide range of devices and varying network speeds |
|
File delivery |
Suitable for streaming in environments with consistent bandwidth |
Effective for on-demand streaming with varying network conditions |
|
Real-time streaming |
Ideal for low-latency real-time streaming, as it maintains a consistent bitrate throughout the stream. |
Suitable for both live and on-demand video streaming services because it strikes a balance between video quality, bandwidth efficiency, and scalability. |
|
Overall flexibility |
Offers limited flexibility in adjusting to varying content. |
Provides flexibility for optimising bitrate based on content complexity. |
|
Complexity of settings |
Simple to set up with fixed bitrate settings. |
Requires understanding of content complexity and appropriate settings. |
When to use CBR vs VBR?
Bandwidth constraints and network conditions
In scenarios where bandwidth is limited or network conditions are unstable, Constant Bitrate (CBR) is the way to go.
- CBR ensures a stable streaming experience, preventing buffering and interruptions even in challenging network environments. If your audience comprises viewers with varying internet speeds, CBR can deliver consistent video quality for all.
- VBR shines in robust network conditions and high-speed connections. With its adaptability, VBR optimises data usage, providing superior video quality when the network permits. Viewers with high-speed internet connections can enjoy higher resolution and clearer visuals, thanks to VBR's dynamic bitrate adjustments.
Video content types
The choice between CBR and VBR should also consider the complexity of your video content.
- For simpler content with consistent scenes, such as podcasts or audio-only streams, CBR is suitable. The fixed bitrate maintains stable quality without compromising on the streaming experience.
- For dynamic content with varying complexities, such as on-demand videos, movies, or TV shows, VBR is the recommended option. Its ability to allocate higher bitrates to complex scenes enhances the visual experience, making it a preferred choice for content with diverse visuals.
CBR or VBR for video streaming
Choosing between CBR and VBR for video streaming depends on factors such as content complexity, audience network conditions, and desired video quality.
As we mentioned earlier, CBR provides a consistent quality but can lead to buffering or stuttering if the viewer's internet connection fluctuates. VBR adjusts quality based on content complexity, providing smoother playback but potentially sacrificing overall quality.
As such, when it comes to VBR vs CBR video - CBR is the best option for live video streaming, whereas VBR is the best option for on-demand video upload.
Recommended encoder settings
There are several popular encoders for video streaming, including x264, x265, and H.266. Each has its own strengths and weaknesses, so it's essential to choose the right one for your specific use case.
General guidelines for setting up CBR and VBR encoding
When setting up CBR and VBR encodes, there are several general guidelines to follow:
- Bitrate targets: Choose an appropriate bitrate target based on the desired video quality and audience expectations.
- Frame rates: Select a frame rate that aligns with the source material and intended display format.
- Resolutions: Choose a resolution that balances video quality and file size.
Tips for optimising encoder settings based on specific use cases
To optimise encoder settings for specific use cases, consider the following tips:
- Low-latency live streams: Use low latency settings and optimised encode presets to minimise delay and ensure real-time video delivery.
- High-quality on-demand content: Use higher bitrates and advanced encode presets to deliver pristine video quality.
By following these guidelines and tips, you can configure your encoder settings to deliver high-quality video streams that meet your audience's expectations.
Digital Samba: elevating your video conferencing experience with CBR and VBR
At Digital Samba, we understand the importance of providing high-quality video conferencing experiences for our users. That's why we leverage WebRTC technology to power our video conferencing platform. WebRTC enables us to deliver reliable, low-latency video streams that are essential for productive virtual meetings and team collaborations.
One of the key advantages of using WebRTC is its ability to automatically adjust video quality based on network conditions. When bandwidth is limited or fluctuating, WebRTC employs Constant Bitrate (CBR) to maintain stable and consistent video quality.
On the other hand, when there's sufficient bandwidth available, WebRTC switches to Variable Bitrate (VBR) to optimize video quality. VBR dynamically adjusts the bitrate of the video stream based on the complexity of the content, ensuring that your videos look great even when sharing dynamic content like presentations or videos.
By leveraging WebRTC's CBR and VBR capabilities, along with our simulcast feature, we provide an unparalleled video conferencing experience tailored to your specific needs.
Trust Digital Samba for an elevated video conferencing experience.
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