reduce some heap use in packet path (#4478)

pkg/sfu/buffer/helpers.go

@@ -162,16 +162,16 @@ func (v *VP8) Unmarshal(payload []byte) error {
 	return nil
 }
 
-func (v *VP8) Marshal() ([]byte, error) {
-	buf := make([]byte, v.HeaderSize)
-	n, err := v.MarshalTo(buf)
+func (v VP8) Marshal() ([]byte, error) {
+	var buf [8]byte
+	n, err := v.MarshalTo(buf[:])
 	if err != nil {
 		return nil, err
 	}
 	return buf[:n], err
 }
 
-func (v *VP8) MarshalTo(buf []byte) (int, error) {
+func (v VP8) MarshalTo(buf []byte) (int, error) {
 	if len(buf) < v.HeaderSize {
 		return 0, errShortPacket
 	}

pkg/sfu/codecmunger/vp8.go

@@ -174,7 +174,7 @@ func (v *VP8) UpdateAndGet(extPkt *buffer.ExtPacket, snOutOfOrder bool, snHasGap
 		// when it reaches a certain size.
 
 		mungedPictureId := uint16((extPictureId - pictureIdOffset) & 0x7fff)
-		vp8Packet := &buffer.VP8{
+		vp8Packet := buffer.VP8{
 			FirstByte:  vp8.FirstByte,
 			I:          vp8.I,
 			M:          mungedPictureId > 127,
@@ -281,7 +281,7 @@ func (v *VP8) UpdateAndGet(extPkt *buffer.ExtPacket, snOutOfOrder bool, snHasGap
 	v.lastTl0PicIdx = mungedTl0PicIdx
 	v.lastKeyIdx = mungedKeyIdx
 
-	vp8Packet := &buffer.VP8{
+	vp8Packet := buffer.VP8{
 		FirstByte:  vp8.FirstByte,
 		I:          vp8.I,
 		M:          mungedPictureId > 127,

pkg/sfu/forwarder.go

@@ -969,18 +969,24 @@ func (f *Forwarder) ProvisionalAllocatePrepare(availableLayers []int32, bitrates
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
-	f.provisional = &VideoAllocationProvisional{
-		allocatedLayer: buffer.InvalidLayer,
-		muted:          f.muted,
-		pubMuted:       f.pubMuted,
-		maxSeenLayer:   f.vls.GetMaxSeen(),
-		bitrates:       bitrates,
-		maxLayer:       f.vls.GetMax(),
-		currentLayer:   f.vls.GetCurrent(),
+	if f.provisional == nil {
+		f.provisional = &VideoAllocationProvisional{}
 	}
 
-	f.provisional.availableLayers = make([]int32, len(availableLayers))
-	copy(f.provisional.availableLayers, availableLayers)
+	p := f.provisional
+	p.allocatedLayer = buffer.InvalidLayer
+	p.muted = f.muted
+	p.pubMuted = f.pubMuted
+	p.maxSeenLayer = f.vls.GetMaxSeen()
+	p.bitrates = bitrates
+	p.maxLayer = f.vls.GetMax()
+	p.currentLayer = f.vls.GetCurrent()
+	if cap(p.availableLayers) >= len(availableLayers) {
+		p.availableLayers = p.availableLayers[:len(availableLayers)]
+	} else {
+		p.availableLayers = make([]int32, len(availableLayers))
+	}
+	copy(p.availableLayers, availableLayers)
 }
 
 func (f *Forwarder) ProvisionalAllocateReset() {
@@ -1811,8 +1817,7 @@ func (f *Forwarder) processSourceSwitch(extPkt *buffer.ExtPacket, layer int32) (
 	//   3. extExpectedTS -> expected timestamp of this packet calculated based on elapsed time since first packet
 	// Ideally, extRefTS and extExpectedTS should be very close and extLastTS should be before both of those.
 	// But, cases like muting/unmuting, clock vagaries, pacing, etc. make them not satisfy those conditions always.
-	rtpMungerState := f.rtpMunger.GetState()
-	extLastTS := rtpMungerState.ExtLastTimestamp
+	extLastTS := f.rtpMunger.GetExtLastTimestamp()
 	extExpectedTS := extLastTS
 	extRefTS := extLastTS
 	refTS := uint32(extRefTS)
@@ -1956,14 +1961,14 @@ func (f *Forwarder) processSourceSwitch(extPkt *buffer.ExtPacket, layer int32) (
 		"switchingAt", switchingAt,
 		"layer", layer,
 		"extLastTS", extLastTS,
-		"lastMarker", rtpMungerState.LastMarker,
+		"lastMarker", f.rtpMunger.GetState().LastMarker,
 		"extRefTS", extRefTS,
 		"dummyStartTSOffset", f.dummyStartTSOffset,
 		"referenceLayerSpatial", f.referenceLayerSpatial,
 		"extExpectedTS", extExpectedTS,
 		"extNextTS", extNextTS,
 		"tsJump", extNextTS-extLastTS,
-		"nextSN", rtpMungerState.ExtLastSequenceNumber+1,
+		"nextSN", f.rtpMunger.GetState().ExtLastSequenceNumber+1,
 		"extIncomingSN", extPkt.ExtSequenceNumber,
 		"extIncomingTS", extPkt.ExtTimestamp,
 		"rtpStats", f.rtpStats,
@@ -2197,7 +2202,7 @@ func (f *Forwarder) GetSnTsForPadding(num int, frameRate uint32, forceMarker boo
 		f.clockRate,
 		frameRate,
 		forceMarker,
-		f.rtpMunger.GetState().ExtLastTimestamp,
+		f.rtpMunger.GetExtLastTimestamp(),
 	)
 }
 
@@ -2212,7 +2217,7 @@ func (f *Forwarder) GetSnTsForBlankFrames(frameRate uint32, numPackets int) ([]S
 		numPackets++
 	}
 
-	extLastTS := f.rtpMunger.GetState().ExtLastTimestamp
+	extLastTS := f.rtpMunger.GetExtLastTimestamp()
 	extExpectedTS := extLastTS
 	if f.rtpStats != nil {
 		tsExt, err := f.rtpStats.GetExpectedRTPTimestamp(mono.Now())

pkg/sfu/rtpmunger.go

@@ -102,6 +102,10 @@ func (r *RTPMunger) GetState() *livekit.RTPMungerState {
 	}
 }
 
+func (r *RTPMunger) GetExtLastTimestamp() uint64 {
+	return r.extLastTS
+}
+
 func (r *RTPMunger) GetTSOffset() uint64 {
 	return r.tsOffset
 }