Video content as we know it goes through some intricate processes before it reaches our screen. Encoding is one of the most essential processes required for delivering high-quality, real-time video.
CBR and VBR are two distinct encoding approaches in the digital media landscape. While CBR holds a steady bitrate ideal for live streaming high-motion content, VBR adapts dynamically to content complexity, perfect for on-demand scenarios.
Let’s compare their key differences and settle the CBR vs VBR debate.
CBR vs. VBR: A side-by side comparison
CBR encoding is ideal for live streaming video content with a higher motion degree. On the other hand, VBR is optimal for delivering content with a lower degree of motion, as it provides better quality at a lower bitrate.
Check out this comparison table to see their key differences and make a better-informed decision about which one to use.
CBR VBR
– Suitable for live stream encoding – Optimal for VOD transcoding
– Wide support and compatibility – Limited support and compatibility
– Delivers consistent results at a preset bitrate – Doesn’t interfere with video quality
– Suitable for time-dependent streams – Good for transcoding without time limits
What is constant bitrate (CBR)?
CBR encoding maintains a consistent bitrate while transmitting data. In simpler terms, the same amount of data is allocated for each second of an audio or video file.
Once you set your bitrate for your CBR-encoded video, it will use the same bitrate for the entire duration, regardless of the size or complexity of the file.
The CBR encoding method is commonly used for live streaming, where a stable bitrate is essential for a smooth playback experience.
CBR video will yield the best results when it’s set up with the correct encoder settings, so make sure to use a higher bitrate. Consequently, your video encoder can work with larger data portions.
Overall, CBR isn’t ideal for data storage, but will excel at encoding video in real time.
CBR use cases
- Streaming services: CBR is often used in live streaming applications where a consistent and predictable data transfer rate is essential for uninterrupted playback. Video streaming platforms, live broadcasts, and online gaming that require a steady flow of data benefit from CBR.
- Telecommunications: VoIP (Voice over Internet Protocol) services and teleconferencing utilize CBR to maintain a consistent quality of service for voice communication. It ensures a steady bitrate, preventing abrupt fluctuations in call quality.
- Broadcasting: Traditional broadcasting, like satellite or cable TV, frequently employs CBR to maintain a constant quality of video/audio for viewers, ensuring a consistent user experience.
- Storage: Certain storage mediums or devices may prefer a constant bitrate to allocate space predictably. CDs, DVDs, and older media formats often utilize CBR to maintain consistent data rates.
Pros of CBR Encoding
- Consistency: CBR provides a steady and predictable bitrate, ensuring a consistent quality of audio or video output. This consistency is particularly valuable in applications where a stable bitrate is necessary for smooth playback or transmission.
- Compatibility: CBR-encoded files tend to be more compatible with older hardware, software, and playback devices. This is because they maintain a fixed bitrate throughout, making them easier to process for systems that might struggle with variable bitrates.
- Simplicity: CBR encoding is simpler in terms of implementation and decoding compared to Variable Bit Rate (VBR). It doesn’t require complex algorithms to adjust the bitrate dynamically based on content complexity, making it easier to manage in certain scenarios.
- Bandwidth Allocation: In situations where bandwidth allocation needs to be consistent and pre-determined, such as in broadcasting or streaming services, CBR ensures a set amount of bandwidth is always available for the content being transmitted.
Cons of CBR Encoding
- Inefficient compression: CBR tends to be less efficient in terms of compression compared to VBR. It allocates the same amount of bits to all parts of the content, regardless of complexity, leading to potential wastage of data on simpler sections.
- Quality sacrifice: In complex scenes or portions of content where more data is needed to maintain high quality, CBR may sacrifice overall quality to adhere to the fixed bitrate, resulting in potential compression artifacts or reduced visual/audio fidelity.
- Bandwidth utilization: CBR doesn’t adapt to fluctuations in available bandwidth. This lack of flexibility can result in underutilization of bandwidth during less complex segments or overload during more complex segments, potentially affecting user experience.
- Storage inefficiency: In scenarios where storage efficiency is crucial, CBR might not be the most efficient method. It may lead to larger file sizes compared to VBR-encoded files, as it doesn’t optimize bitrate allocation based on content complexity.
What is variable bitrate (VBR)?
Contrastingly, VBR encoding will dynamically adjust the bitrate depending on the complexity of the content. Unlike CBR, VBR switches to a higher bitrate for more detailed scenes, while using a lower bitrate during simpler sections. This results in uncompromised quality and an optimized file size.
On-demand video transcoding could benefit the most from VBR due to its flexibility. However, since VBR processes data longer, it’s not a great fit for live streaming.
There are three types of VBR:
- Quality VBR: Encodes data with single-pass encoding.
- Unconstrained VBR: Takes advantage of multi-pass encoding to determine the best available streaming quality while preserving the average bitrate.
- Constrained VBR: Also uses multi-pass encoding, but decides how to encode the data according to the maximum bitrate and maximum buffer window.
VBR use cases
- Compression efficiency: VBR is useful in scenarios where maximizing compression efficiency is crucial. It dynamically allocates more bits to complex or detailed parts of the content and fewer bits to simpler parts, resulting in better quality for the same file size compared to CBR.
- Multimedia streaming: VBR is advantageous in streaming situations where bandwidth availability varies. It optimizes the quality by allocating more bits to complex scenes and fewer bits to simpler ones, adjusting to available bandwidth without sacrificing quality.
- Optimized file sizes: When file size is a concern but maintaining quality is crucial, VBR is a suitable choice. It allows for better compression in sections of the content that do not require high bitrate, reducing the overall file size while maintaining quality.
- Digital storage: VBR is beneficial in digital storage applications where maximizing storage space is essential. It helps to reduce the file size without compromising quality significantly.
Pros of VBR Encoding
- Improved compression efficiency: VBR adjusts the bitrate dynamically based on the complexity of the content. It allocates more bits to complex scenes and fewer bits to simpler ones, resulting in better compression efficiency compared to CBR encoding.
- Enhanced quality: VBR often maintains higher quality in encoded files compared to CBR. By allocating more bits to complex parts of the content, it preserves detail and reduces compression artifacts, leading to better overall quality.
- Optimized file sizes: VBR can produce smaller file sizes while maintaining comparable or better quality than CBR. It optimizes bitrate allocation, resulting in more efficient use of data and reduced storage requirements.
- Adaptability to content complexity: VBR adapts dynamically to varying complexities within the content. It adjusts the bitrate according to the requirements of each scene or segment, ensuring better visual/audio fidelity where it’s needed most.
Cons of VBR Encoding
- Complexity and compatibility: VBR encoding is more complex than CBR, requiring algorithms to analyze content and allocate bitrates dynamically. This complexity might lead to compatibility issues with older or less sophisticated playback devices or software.
- Unpredictability: While VBR provides better compression efficiency, the variability in bitrate can be less predictable compared to CBR. This variability might not be suitable for applications where a consistent bitrate is necessary for seamless playback or transmission.
- Resource intensive encoding: VBR encoding requires more computational resources and time compared to CBR. Analyzing content complexity and dynamically adjusting bitrates can be more resource-intensive, impacting encoding speed.
- Bandwidth fluctuation challenges: In streaming scenarios with constrained or fluctuating bandwidth, VBR may pose challenges. It might adapt by utilizing more bandwidth for complex scenes, potentially causing buffering or quality fluctuations if bandwidth availability changes abruptly.
Bottom line
The choice between CBR and VBR will ultimately depend on the type of content you wish to stream.
Hopefully, our article helped you recognize how both methods compare and prepared you for your live streaming journey.
JW Player is a great starting point, whether you’re just getting started with live streaming or you already have broadcasting experience. Contact us today to learn more about our solution!