snapshot of https://github.com/livekit/livekit.git @ 08c5433449c106943231037d0b892895f6e92d3b (2026-09-15)

pkg/sfu/videolayerselector/simulcast_test.go

@@ -0,0 +1,77 @@
+// Copyright 2026 LiveKit, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package videolayerselector
+
+import (
+	"testing"
+
+	"github.com/pion/rtp"
+	"github.com/stretchr/testify/require"
+
+	"github.com/livekit/livekit-server/pkg/sfu/buffer"
+	"github.com/livekit/protocol/logger"
+)
+
+func keyFrameOnLayer(spatial, temporal int32) *buffer.ExtPacket {
+	return &buffer.ExtPacket{
+		VideoLayer: buffer.VideoLayer{Spatial: spatial, Temporal: temporal},
+		Packet:     &rtp.Packet{},
+		IsKeyFrame: true,
+	}
+}
+
+// On initial acquisition the selector must latch directly onto the target layer and ignore
+// lower-layer key frames that arrive first, so a subscriber requesting the top layer does not
+// briefly decode a lower layer (a visible quality ramp).
+func TestSimulcastSelectAcquiresTargetLayerDirectly(t *testing.T) {
+	s := NewSimulcast(logger.GetLogger())
+	s.SetEnableStartAtDesiredQuality(true)
+	s.SetMax(buffer.VideoLayer{Spatial: 2, Temporal: 2})
+	s.SetMaxSeen(buffer.VideoLayer{Spatial: 2, Temporal: 2})
+	s.SetTarget(buffer.VideoLayer{Spatial: 2, Temporal: 2})
+	s.SetRequestSpatial(2)
+	s.SetCurrent(buffer.InvalidLayer)
+
+	// lower-layer key frames arriving first must NOT be latched
+	require.False(t, s.Select(keyFrameOnLayer(0, 2), 0).IsSelected)
+	require.False(t, s.GetCurrent().IsValid())
+	require.False(t, s.Select(keyFrameOnLayer(1, 2), 1).IsSelected)
+	require.False(t, s.GetCurrent().IsValid())
+
+	// the target layer key frame latches directly
+	require.True(t, s.Select(keyFrameOnLayer(2, 2), 2).IsSelected)
+	require.Equal(t, int32(2), s.GetCurrent().Spatial)
+}
+
+// Acquisition follows whatever target the allocator set: when the target is lowered (e.g. the
+// acquisition grace expired and the allocator fell back to the highest layer seen), the selector
+// latches that lower layer directly. This is the fallback path that prevents a stall when the
+// originally requested layer never shows up.
+func TestSimulcastSelectAcquiresLoweredTarget(t *testing.T) {
+	s := NewSimulcast(logger.GetLogger())
+	s.SetEnableStartAtDesiredQuality(true)
+	s.SetMax(buffer.VideoLayer{Spatial: 2, Temporal: 2})
+	s.SetMaxSeen(buffer.VideoLayer{Spatial: 1, Temporal: 2})
+	// allocator dropped the target to the highest layer actually seen
+	s.SetTarget(buffer.VideoLayer{Spatial: 1, Temporal: 2})
+	s.SetRequestSpatial(1)
+	s.SetCurrent(buffer.InvalidLayer)
+
+	require.False(t, s.Select(keyFrameOnLayer(0, 2), 0).IsSelected)
+	require.False(t, s.GetCurrent().IsValid())
+
+	require.True(t, s.Select(keyFrameOnLayer(1, 2), 1).IsSelected)
+	require.Equal(t, int32(1), s.GetCurrent().Spatial)
+}