Constant Bitrate (CBR)

Imagine watching a live stream with a lot of buffering and inconsistent streaming. That creates a lousy watching experience for end users. For consistent and seamless activity streaming and video export, livestreaming applications can incorporate CBR.

What is CBR?

CBR is a video encoding architecture that processes audio/video data at a constant rate over a certain period. This means the number of bits to be transferred during the entire audio or video playback remains unchanged. For instance, a video with a constant bit rate of 25 Mbps will retain the same amount of bits from the beginning to its end.

The video loads and plays quickly since the number of bits from the beginning to the end remains unchanged. Another benefit of using CBR is that it makes a video easy to play on different devices.

How does CBR Work?

The quality of images and video is determined by the number of bits transmitted per second, called bitrate. In real-time video communication, for example, the number of bits transferred per second can be configured to be constant. Using CBR in this context means the video quality remains the same no matter what happens.

Benefits of CBR

• It ensures total control over bandwidth in a network.
• It is faster to encode than VBR.
• It provides a more predictable network than VBR.

Application Areas of CBR

• Low-latency streaming: In services like livestreaming, CBR helps maintain consistent latency.
• Fixed bandwidth requirement: Certain livestreaming services in which changing the bandwidth is not necessary may benefit from CBR to ensure smooth media delivery and prevent video buffering issues.
• Audio Streaming: In audio streaming services, such as internet radio or podcasting, constant bitrate encoding ensures a consistent audio quality throughout the stream. This is important for maintaining a smooth listening experience without fluctuations in audio quality.
• Voice over IP (VoIP): In VoIP applications like Skype, Zoom, or business telephony systems, constant bitrate encoding helps ensure clear and consistent voice communication. It minimizes variations in voice quality caused by fluctuations in network conditions.
• Live Broadcasting: In live broadcasting scenarios, such as television or radio broadcasts, constant bitrate encoding ensures a steady stream of data to viewers or listeners. This helps maintain a consistent viewing or listening experience without interruptions or quality fluctuations.
• Video Conferencing: In video conferencing applications like Microsoft Teams, Zoom, or Google Meet, constant bitrate encoding delivers a stable and reliable video stream to participants. This helps prevent abrupt changes in video quality during the conference call.

Real-World Examples of Constant Bitrate

• Live audio room applications: Audio room applications like X Spaces and Clubhouse often use CBR to ensure consistent audio quality for end users. CBR minimizes interruptions and buffering for users with poor network conditions.
• Real-time video conferencing: In conditions of unstable internet connections, a platform like Zoom might use CBR to ensure a continuous connection and avoid overload of video feeds.
• Digital Broadcasting: In digital broadcasting standards like DVB (Digital Video Broadcasting) or ATSC (Advanced Television Systems Committee), constant bitrate encoding is often used for transmitting television and radio signals over the air. It ensures consistent service to viewers and listeners, even in challenging reception conditions.
• Streaming Video-on-Demand (VOD): In streaming services like Netflix, Amazon Prime Video, or Hulu, constant bitrate encoding is employed to deliver a consistent video streaming experience to users. It helps maintain a steady playback quality without buffering or quality fluctuations.
• CD Audio: In audio CDs, constant bitrate encoding stores audio tracks with a fixed bitrate. This ensures consistent audio quality.

Constant vs Variable Bitrate (VBR)

Since the bitrate remains constant when a network becomes busy and unbusy, it may reduce the quality of video applications. CBR also uses excessive data storage that a particular scene may not require.

The table below distinguishes between CBR and VBR.

Feature	CBR	VBR
Bitrate	Remains constant regardless of the network condition	Reduces and increases to adapt to network load
Quality	Offers consistent and predictable quality	Offers variable quality (low and high)
Use case	It is ideal for fulfilling low-latency requirements in live activity streaming applications like Twitch.	It is ideal for high-quality video calls like in FaceTime.
Complexity	It is simple and efficient	Adjusting the bitrate from time to time creates complexity.

Frequently Asked Questions