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Declare one spatial layer per stream for single-track video publishes #1045

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Declare one spatial layer per stream for single-track video publishes #1045

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dadfcb8
Declare one spatial layer per stream for single-track video publishes
pabloFuente Oct 22, 2026
4dad01a
Limit the one-spatial-layer declaration to sample tracks
pabloFuente Oct 22, 2026
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17 changes: 13 additions & 4 deletions localparticipant.go
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Original file line number Diff line number Diff line change
Expand Up @@ -164,14 +164,16 @@ func (p *LocalParticipant) prepareTrackPublication(track webrtc.TrackLocal, opts
if primaryCodec.MimeType != "" && (kind == TrackKindVideo || withBackupCodec) {
req.SimulcastCodecs = []*livekit.SimulcastCodec{
{
Codec: primaryCodec.MimeType,
Cid: track.ID(),
Codec: primaryCodec.MimeType,
Cid: track.ID(),
VideoLayerMode: sampleTrackLayerMode(kind, track),
},
}
if withBackupCodec {
req.SimulcastCodecs = append(req.SimulcastCodecs, &livekit.SimulcastCodec{
Codec: pubOptions.backupCodecTrack.Codec().MimeType,
Cid: pubOptions.backupCodecTrack.ID(),
Codec: pubOptions.backupCodecTrack.Codec().MimeType,
Cid: pubOptions.backupCodecTrack.ID(),
VideoLayerMode: sampleTrackLayerMode(kind, pubOptions.backupCodecTrack),
})
pub.setBackupCodecTrack(pubOptions.backupCodecTrack)
}
Expand All @@ -181,6 +183,13 @@ func (p *LocalParticipant) prepareTrackPublication(track webrtc.TrackLocal, opts
return pub, req, nil
}

func sampleTrackLayerMode(kind TrackKind, track webrtc.TrackLocal) livekit.VideoLayer_Mode {
if _, ok := track.(*LocalTrack); ok && kind == TrackKindVideo {
return livekit.VideoLayer_ONE_SPATIAL_LAYER_PER_STREAM
}
return livekit.VideoLayer_MODE_UNUSED
Comment on lines +187 to +190

@devin-ai-integration devin-ai-integration Bot Oct 22, 2026

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🔴 Single-layer external tracks declared as SVC

For a single-layer VP9 or AV1 TrackLocalStaticSample, sampleTrackLayerMode returns MODE_UNUSED because it is not *LocalTrack. The server infers multiple spatial layers, mislabeling the primary or backup video stream as SVC.

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PublishTrack accepts any webrtc.TrackLocal, and prepareTrackPublication declares the codec for external tracks implementing TrackLocalWithCodec. The server infers multiple spatial layers for VP9 and AV1 when VideoLayerMode is unset. The concrete type test only recognizes SDK LocalTrack, so a single-layer Pion sample track gets an unset mode even though its samples contain only one spatial layer. The backup codec entry uses the same helper.

Example: Publish a VP9 webrtc.TrackLocalStaticSample with ordinary single-layer samples. Its codec is declared, but its video layer mode is unset; the server reports MULTIPLE_SPATIAL_LAYERS_PER_STREAM rather than ONE_SPATIAL_LAYER_PER_STREAM.

Recommended fix: Set ONE_SPATIAL_LAYER_PER_STREAM for known single-layer sample tracks beyond *LocalTrack, including Pion's static sample tracks. Preserve an explicit route for external tracks that genuinely carry SVC if that behavior is required.

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}

func (p *LocalParticipant) notifyTrackPublished(pub *LocalTrackPublication) {
p.Callback.OnLocalTrackPublished(pub, p)
p.roomCallback.OnLocalTrackPublished(pub, p)
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