MSC4195: LiveKit transport for MatrixRTC

[hughns]

Rendered

Server

• m.livekit in /transports: Add support for specifying the SFU WebSocket URL together with configured LiveKit transports element-hq/synapse#20146

Note

For backwards compatibility, the endpoint also returns livekit_service_url. The stems from a previous iteration of the proposal and has been fully replaced by url in the current text.

• Client-Server & Server-Server endpoints: https://github.com/element-hq/lk-jwt-service implements the endpoints introduced by this proposal. People interested in reviewing the implementation should start in https://github.com/element-hq/lk-jwt-service/blob/main/src/handler.rs#L1245. The service is integrated into https://github.com/element-hq/synapse/ as an application service by means of:
  • Add experimental support for letting application services proxy namespaces in the C-S and S-S API as per MSC4512 element-hq/synapse#19972
  • Add experimental support for sending federation requests from app services as per MSC4512 element-hq/synapse#19977
  • Add experimental support for MSC4502: Targeted and unrestricted room member queries element-hq/synapse#19974.
• The three pull requests above depend on MSC4512 and MSC4502. This is an implementation detail of the Synapse implementation, however. There is no dependency between the current proposal and these two MSCs.

Note

For backwards compatibility with implementations of previous versions of this MSC, https://github.com/element-hq/lk-jwt-service exhibits the following differences with respect to the proposal text:

• The legacy endpoints /sfu/get, /get_token and /delegate_delayed_leave are still included. These have been replaced by proper Client-Server and Server-Server endpoints in the proposal which are also implemented in https://github.com/element-hq/lk-jwt-service.
• The device ID is still included in the LiveKit participant identity derivation. On requests, the ID is supplied as claimed_device_id wrapped together with the member ID in a member object. The proposal has eliminated claimed_device_id and replaced the member object with member_id.
• The delay_timeout request parameter is still included in the /delegate_delayed_leave endpoint. This parameter has been removed from the proposal because it can be inferred from the delayed event ID.
• Extended tokens do not contain the grant to create LiveKit rooms. Instead the service creates rooms itself (using its own token). This is because client implementations are not yet updated to perform the room creation themselves.

Furthermore, https://github.com/element-hq/lk-jwt-service doesn't currently implement kicking participants from the SFU on room leaves.

Client

• LiveKit participant identity derivation: Adapt LiveKit Identity hash calculation to latest MSC4195 update matrix-js-sdk#5268
• Initial multi-SFU implementation: A new world: "Multi-SFU" media transport element-hq/element-call#3512
• Taking the LiveKit room name from the JWT access token: The advertised livekit_alias in membership is deprecated element-hq/element-call#3706
• Switch to Client-Server endpoints for token requests: Add livekit rtc cs api endpoints to client (and embedded client) matrix-js-sdk#5496
• Delegation of delayed leave events: Delegate delayed events using dedicated endpoint element-hq/element-call#4209

Note

Similar to what's mentioned above, the client implementations also still support the legacy livekit_service_url property in transports objects in membership events.

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SCT Stuff:

No MSC checklist

No FCP tickyboxes

BLOCKED on MSC4143 - #4195 (comment)