When creating the LiveKit Room, enable Dynacast (dynamic broadcasting) in RoomOptions; this causes the SFU to pause simulcast layers that no subscribers are consuming.
Publish video from the client SDK with simulcast enabled in TrackPublishOptions; by default, three spatial layers are produced (e.g. 180p, 360p, 720p) as separate RTP streams.
The SFU automatically selects which simulcast layer to forward to each subscriber based on the subscriber's available downstream bandwidth, estimated via REMB and TWCC feedback.
To customize layer dimensions and bitrates, set the videoSimulcastLayers array in TrackPublishDefaults; you can specify up to two additional layers beyond the base.
For VP9 or AV1, use SVC (Scalable Video Coding) scalability modes instead of simulcast; set scalabilityMode in TrackPublishOptions — simulcast layers have no effect for SVC codecs.
Subscribers can request a specific maximum layer via setVideoQuality on the RemoteTrackPublication to pin to a desired resolution regardless of automatic selection.
Known gotchas
Dynacast pauses the high-resolution layer when only lower-resolution subscribers are present, reducing bandwidth and CPU; re-enabling a paused layer has a brief ramp-up delay as keyframes are produced.
Simulcast with H.264 may have browser compatibility variations; VP8 is the most universally supported codec for multi-layer simulcast in browsers.
SVC codecs (VP9/AV1) and simulcast are mutually exclusive in LiveKit; do not set both simulcast:true and an SVC scalabilityMode on the same track.
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