Plan B was an early proposal for handling multiple media sources in WebRTC SDP. It has been deprecated in favor of Unified Plan.
What Plan B was
Plan B used a single m= line per media type (one for all audio, one for all video) with multiple SSRC values within each m= line to represent different sources. This was Chrome’s original approach to handling multiple media streams.
Why Plan B was replaced
Plan B was replaced by Unified Plan because:
- It was not formally standardized by the IETF
- Firefox and Safari implemented Unified Plan, causing interoperability issues
- Unified Plan (one m= line per media track) is more flexible and aligns with the JSEP specification better
- It complicated SFU implementations that needed to manipulate individual tracks
Chrome removed Plan B support, and all modern WebRTC applications should use Unified Plan exclusively. Legacy applications that relied on Plan B need to be migrated.
