Bitrate is the amount of data processed per unit of time in a media stream, typically measured in kilobits per second (kbps) or megabits per second (Mbps).
In WebRTC, bitrate is a key metric that directly affects media quality. The BWE (Bandwidth Estimation) algorithm continuously adjusts the encoding bitrate based on available network bandwidth.
Typical WebRTC bitrates
Audio (Opus):
- Speech: 16-32 kbps
- High quality voice: 32-64 kbps
- Music: 64-128 kbps
Video:
- 360p: 300-600 kbps
- 720p (HD): 1-2 Mbps
- 1080p: 2-4 Mbps
- Screen sharing: 500 kbps – 3 Mbps (varies with content)
CBR vs VBR
- CBR (Constant Bitrate): Encoder maintains a fixed bitrate. Simpler for bandwidth management
- VBR (Variable Bitrate): Encoder uses more bits for complex scenes and fewer for simple ones. Better quality per bit
WebRTC typically uses VBR, allowing the encoder to allocate bits efficiently. The BWE algorithm sets the maximum bitrate ceiling, and the encoder operates within that constraint.
