General definition
Simulcast solves the group video call problem: participants join on connections ranging from high-speed fibre to a congested mobile network. Without simulcast, the publisher must choose one encode quality, meaning either low-bandwidth participants drop frames or high-bandwidth participants receive a lower-quality stream than their connection can support.
- Publisher sends two or three independent encoded layers (for example 1080p, 360p, and 180p)
- SFU receives all layers and forwards the most appropriate one per subscriber
- The receiving layer switches automatically as network conditions change
- No re-encoding happens at the SFU, so CPU cost stays low
Simulcast is a core feature of the WebRTC specification and is supported by all major browsers. It works in combination with bandwidth estimation (REMB/TWCC) to enable smooth adaptive quality. The alternative, SVC (Scalable Video Coding), achieves similar goals with a single layered bitstream rather than multiple independent streams.
In the Ethora ecosystem
Ethora’s voice and video calling is built on WebRTC with an SFU architecture, enabling simulcast for group calls. Each participant receives the video layer that matches their connection rather than the lowest common denominator, which is especially important for enterprise and healthcare group meetings where participants join from diverse network conditions.
In a self-hosted Ethora deployment, simulcast configuration is fully accessible, allowing infrastructure teams to tune the number of layers and bitrate targets to match the organisation’s bandwidth profile and quality requirements.
