Timo K.
d0a2ff12f1
The session speaks MatrixRTC and sees media through MediaBackend in sdk/src/backend/api.ts. Everything LiveKit lives in sdk/src/backend/livekit/, the only place in the SDK that imports livekit-client; the import boundary rule now enforces that outside sdk/src/backend/ the LiveKit packages appear in type imports only. The seam sits above the connection manager: one connection per transport url is the LiveKit multi-SFU strategy, not a MatrixRTC concept, so a cascading SFU or full mesh replaces the folder, not the session. A backend prepares the local transport the session discovered (the token exchange and the delegation probe, reported as canDelegateDelayedLeave), hands the delayed leave over per delay id, gives the local member one publish switch plus publish/unpublish, builds a remote member's media from its membership and registers that membership's transport for as long as the member lives, and reports its connections for the transport registry, which keys on the raw transport serialised with sorted keys. The backend's context carries no Matrix client (a backend picks what it calls in its own options), no membership list, and no js-sdk session: media keys arrive as a stream replayed on subscribe, and MatrixKeyProvider subscribes to it. The MatrixRTC mode no longer reaches LiveKit; it becomes a tokenEndpoint choice made where the default backend is built. Two behaviour changes ride along. Publishing is one boolean, joined and homeserver reachable, where before a sync hiccup after leave() resumed the upstream of tracks that were meant to stay silent. And ResolvedConnection keeps one ResolvedTransport object per fetch, so a state change no longer reads as a change of what was fetched. MatrixRTCClientOptions gains backend?: MediaBackendFactory, defaulting to createLivekitBackend built from the client options. authenticateWithTransport takes tokenEndpoint instead of matrixRTCMode.
MatrixRTC SDK (EXPERIMENTAL)
@element-hq/matrixrtc-sdk is the call model under Element Call, on its own:
MatrixRTC memberships and transports, media connections, publishing, E2EE keys and
the media of every member, as observables. It has no UI. Element Call's own
CallViewModel is meant to become one consumer of it. The design is in
SdkArchitecture.md, the migration from the view model
in SdkMigration.md. Media goes through one media backend
behind MediaBackend; LiveKit, under src/backend/livekit/, is the only one
today and the only place that imports livekit-client.
Status: first implementation. createMatrixRTCClient joins the session, connects to
the transport, publishes the local media and exposes every member's media; the
development harness and its e2e tests in playwright/sdk drive it, and Element
Call's own CallViewModel is built on it. It depends on nothing in Element Call's
src/.
Using it
import {
constant,
createMatrixRTCClient,
E2eeType,
MatrixRTCMode,
ObservableScope,
} from "@element-hq/matrixrtc-sdk";
const scope = new ObservableScope();
const rtcClient = createMatrixRTCClient(
scope,
client, // a matrix-js-sdk MatrixClient, logged in and syncing
room, // the matrix-js-sdk Room, from client.getRoom() once the join has synced
{
publish: [{ source: "microphone" }, { source: "camera" }],
audioOutputDeviceId$: constant(undefined),
},
{
encryptionSystem: { kind: E2eeType.PER_PARTICIPANT },
matrixRTCMode: MatrixRTCMode.Compatibility,
},
);
rtcClient.join();
rtcClient.remoteMembers$.subscribe((members) => {
// each member has displayName$, media$ and more; a media track is rendered
// by handing it a <video> or <audio> element: track.attach(element)
});
// later
rtcClient.leave();
scope.end();
dev/main.ts is this example as a working page.
Development
Everything runs from the repository root. This directory is a pnpm project of its
own only so that a host can install it as a git dependency (see
pnpm-workspace.yaml).
pnpm dev:sdk # the harness, https://localhost:3002
pnpm build:sdk # dist/matrixrtc-sdk.js and dist/types
pnpm test:playwright playwright/sdk # needs `pnpm backend`
Installing
pnpm add github:element-hq/element-call#<ref>&path:/sdk
The host supplies matrix-js-sdk, livekit-client and rxjs; the build leaves
them external.