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

pkg/sfu/videolayerselector/framenumberwrapper.go

@@ -0,0 +1,58 @@
+// Copyright 2024 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 "github.com/livekit/protocol/logger"
+
+type FrameNumberWrapper struct {
+	offset uint64
+	last   uint64
+	inited bool
+	logger logger.Logger
+}
+
+// UpdateAndGet returns the wrapped frame number from the given frame number, and updates the offset to
+// make sure the returned frame number is always inorder. Should only updateOffset if the new frame is a keyframe
+// because frame dependencies uses on the frame number diff so frames inside a GOP should have the same offset.
+func (f *FrameNumberWrapper) UpdateAndGet(new uint64, updateOffset bool) uint64 {
+	if !f.inited {
+		f.last = new
+		f.inited = true
+		return new
+	}
+
+	if new <= f.last {
+		return new + f.offset
+	}
+
+	if updateOffset {
+		new16 := uint16(new + f.offset)
+		last16 := uint16(f.last + f.offset)
+		// if new frame number wraps around and is considered as earlier by client, increase offset to make it later
+		if diff := new16 - last16; diff > 0x8000 || (diff == 0x8000 && new16 < last16) {
+			// increase offset by 6000, nearly 10 seconds for 30fps video with 3 spatial layers
+			prevOffset := f.offset
+			f.offset += uint64(65535 - diff + 6000)
+
+			f.logger.Debugw("wrap around frame number seen, update offset", "new", new, "last", f.last, "offset", f.offset, "prevOffset", prevOffset, "lastWrapFn", last16, "newWrapFn", new16)
+		}
+	}
+	f.last = new
+	return new + f.offset
+}
+
+func (f *FrameNumberWrapper) LastOrigin() uint64 {
+	return f.last
+}