Unified Plan is an IETF draft proposal for signaling multiple media sources in SDP.

Signaling multiple media sources is needed to be able to send a video along with screen sharing, multiple camera sources or routing multiple streams from an SFU to the users.

In Unified Plan, there is an m= line per each media source.

The mechanism chosen for the official WebRTC specification is Unified Plan. The competing approach is known as Plan B.

Today, all browsers support it by default.

Signaling Multiple Media Sources

In multiparty real-time communication setup (most group calling solutions), the ability to handle multiple media sources is important.

This includes the capability to send a video alongside screen sharing, managing multiple camera sources, or routing multiple streams from a Selective Forwarding Unit (SFU) to the users.

The necessity for a standardized plan arose from the need to ensure seamless interaction among these media elements, and thus, the Unified Plan was conceived.

Structure

The core structure is defined by the presence of an m= line for each media source within the SDP.

This m= line is a fundamental aspect as it delineates each media source, thereby facilitating the organized signaling of multiple media streams.

The structuring is what sets Unified Plan apart and aligns it with the official WebRTC specification.

Adoption and Browser Support

Unified Plan, over time, has garnered widespread adoption and has become the mechanism of choice as per the official WebRTC specification, superseding the competing (and not deprecated or unimplemented) approach known as Plan B.

The transition was driven by its robust structure and the ease it introduced in managing multiple media sources.