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61 lines
2.7 KiB
Markdown
61 lines
2.7 KiB
Markdown
# MatrixRTC modes
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Element Call is in the middle of a transition of how a call session is
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represented and how participants pick an SFU:
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- **Membership events**: from room _state_ events
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(`org.matrix.msc3401.call.member`) to _sticky_ events
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([MSC4354](https://github.com/matrix-org/matrix-spec-proposals/pull/4354)),
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which are a much better fit for the short lived, per-device nature of call
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memberships.
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- **SFU selection**: from "everyone connects to the SFU of the oldest member" to
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**multi SFU**, where each participant uses its own homeserver's SFU and the
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SFUs interconnect.
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Not every homeserver supports sticky events yet. Multi SFU is supported on all current (August 2026)
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element call clients. The three MatrixRTC modes are the steps of that transition,
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so a deployment can pick the newest one its homeserver and its user base can
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handle.
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## The modes
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| Mode | Membership events | SFU selection | JWT endpoint |
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| --------------- | ----------------- | ------------- | ---------------------------- |
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| `legacy` | state events | oldest member | legacy |
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| `compatibility` | state events | multi SFU | legacy |
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| `matrix_2_0` | sticky events | multi SFU | Matrix 2.0 (hashed identity) |
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**`legacy`** — the lowest common denominator. Use it if calls need to work with
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Element Call clients older than v0.17.0, which cannot handle multi SFU calls. (unused)
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**`compatibility`** — multi SFU, but still state events. Use it when all Element
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Call clients are v0.17.0 or later but the homeserver does not support sticky
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events. This is the default. (default)
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**`matrix_2_0`** — the target state. Requires a homeserver that advertises
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MSC4354 and all clients on v0.17.0 or later. The local membership requests its
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token from the Matrix 2.0 JWT endpoint of the
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[MatrixRTC Authorization Service](https://github.com/element-hq/lk-jwt-service)
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and identifies the room by a hashed identity instead of a `livekit_alias`.
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(Remote memberships always try the new endpoint first and fall back to the
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legacy one, so remote participants can be on either.)
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## Selecting a mode
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Users can choose a mode under **Settings → Developer → MatrixRTC mode**. The
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Matrix 2.0 option is disabled if the homeserver does not support sticky events.
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A deployment can pin the mode for all its clients in `config.json`, which
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disables the Developer Settings choice:
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```json
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{
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"matrix_rtc_mode": "compatibility"
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}
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```
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Valid values are `legacy`, `compatibility` and `matrix_2_0`; an invalid value is
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ignored (with a warning) and the user's choice applies. Pinning `matrix_2_0` on a
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homeserver without sticky event support makes joining fail with a "sticky events
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required" error.
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