Scalable video coding (SVC).

conn/conn.go

@@ -40,5 +40,5 @@ type DownTrack interface {
 	Write(buf []byte) (int, error)
 	SetTimeOffset(ntp uint64, rtp uint32)
 	SetCname(string)
-	GetMaxBitrate() uint64
+	GetMaxBitrate() (uint64, int)
 }

diskwriter/diskwriter.go

@@ -618,6 +618,6 @@ func (conn *diskConn) initWriter(width, height uint32) error {
 	return nil
 }
 
-func (t *diskTrack) GetMaxBitrate() uint64 {
-	return ^uint64(0)
+func (t *diskTrack) GetMaxBitrate() (uint64, int) {
+	return ^uint64(0), -1
 }

go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/gorilla/websocket v1.4.2
 	github.com/pion/ice/v2 v2.1.7
 	github.com/pion/rtcp v1.2.6
-	github.com/pion/rtp v1.6.2
+	github.com/pion/rtp v1.6.6-0.20210512022946-4e87540a7fe6
 	github.com/pion/sdp/v3 v3.0.4
 	github.com/pion/turn/v2 v2.0.5
 	github.com/pion/webrtc/v3 v3.0.27

go.sum

@@ -51,8 +51,9 @@ github.com/pion/randutil v0.1.0 h1:CFG1UdESneORglEsnimhUjf33Rwjubwj6xfiOXBa3mA=
 github.com/pion/randutil v0.1.0/go.mod h1:XcJrSMMbbMRhASFVOlj/5hQial/Y8oH/HVo7TBZq+j8=
 github.com/pion/rtcp v1.2.6 h1:1zvwBbyd0TeEuuWftrd/4d++m+/kZSeiguxU61LFWpo=
 github.com/pion/rtcp v1.2.6/go.mod h1:52rMNPWFsjr39z9B9MhnkqhPLoeHTv1aN63o/42bWE0=
-github.com/pion/rtp v1.6.2 h1:iGBerLX6JiDjB9NXuaPzHyxHFG9JsIEdgwTC0lp5n/U=
 github.com/pion/rtp v1.6.2/go.mod h1:bDb5n+BFZxXx0Ea7E5qe+klMuqiBrP+w8XSjiWtCUko=
+github.com/pion/rtp v1.6.6-0.20210512022946-4e87540a7fe6 h1:xAaGxAEYiL96TRp4DhhrrH7JRLBuLM+nGqhOXnWzTBs=
+github.com/pion/rtp v1.6.6-0.20210512022946-4e87540a7fe6/go.mod h1:bDb5n+BFZxXx0Ea7E5qe+klMuqiBrP+w8XSjiWtCUko=
 github.com/pion/sctp v1.7.10/go.mod h1:EhpTUQu1/lcK3xI+eriS6/96fWetHGCvBi9MSsnaBN0=
 github.com/pion/sctp v1.7.12 h1:GsatLufywVruXbZZT1CKg+Jr8ZTkwiPnmUC/oO9+uuY=
 github.com/pion/sctp v1.7.12/go.mod h1:xFe9cLMZ5Vj6eOzpyiKjT9SwGM4KpK/8Jbw5//jc+0s=

group/group.go

@@ -61,8 +61,8 @@ type ChatHistoryEntry struct {
 }
 
 const (
-	LowBitrate = 100000
-	MinBitrate = 2 * LowBitrate
+	LowBitrate = 100 * 1024
+	MinBitrate = LowBitrate * 2
 )
 
 type Group struct {

packetmap/packetmap.go

+// Package packetmap implements remapping of sequence numbers and picture ids.
+package packetmap
+
+import (
+	"sync"
+)
+
+const maxEntries = 128
+
+type Map struct {
+	mu        sync.Mutex
+	next      uint16
+	nextPid   uint16
+	delta     uint16
+	pidDelta  uint16
+	lastEntry uint16
+	entries   []entry
+}
+
+type entry struct {
+	first, count uint16
+	delta        uint16
+	pidDelta     uint16
+}
+
+// Map maps a seqno, adding the mapping if required.  It returns whether
+// the seqno could be mapped, the target seqno, and the pid delta to apply.
+func (m *Map) Map(seqno uint16, pid uint16) (bool, uint16, uint16) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.delta == 0 && m.entries == nil {
+		m.next = seqno + 1
+		m.nextPid = pid
+		return true, seqno, 0
+	}
+
+	if compare(m.next, seqno) <= 0 {
+		if uint16(seqno-m.next) > 8*1024 {
+			m.reset()
+			m.next = seqno + 1
+			m.nextPid = pid
+			return true, seqno, 0
+		}
+		addMapping(m, seqno, pid, m.delta, m.pidDelta)
+		m.next = seqno + 1
+		m.nextPid = pid
+		return true, seqno + m.delta, m.pidDelta
+	}
+
+	if uint16(m.next-seqno) > 8*1024 {
+		m.reset()
+		m.next = seqno + 1
+		m.nextPid = pid
+		return true, seqno, 0
+	}
+
+	return m.direct(seqno)
+}
+
+func (m *Map) reset() {
+	m.next = 0
+	m.nextPid = 0
+	m.delta = 0
+	m.pidDelta = 0
+	m.lastEntry = 0
+	m.entries = nil
+}
+
+func addMapping(m *Map, seqno, pid uint16, delta, pidDelta uint16) {
+	if len(m.entries) == 0 {
+		m.entries = []entry{
+			entry{
+				first:    seqno,
+				count:    1,
+				delta:    delta,
+				pidDelta: pidDelta,
+			},
+		}
+		return
+	}
+
+	i := m.lastEntry
+	if delta == m.entries[i].delta && pidDelta == m.entries[i].pidDelta {
+		m.entries[m.lastEntry].count = seqno - m.entries[i].first + 1
+		return
+	}
+
+	e := entry{
+		first:    seqno,
+		count:    1,
+		delta:    delta,
+		pidDelta: pidDelta,
+	}
+
+	if len(m.entries) < maxEntries {
+		m.entries = append(m.entries, e)
+		m.lastEntry = uint16(len(m.entries) - 1)
+		return
+	}
+
+	j := (m.lastEntry + 1) % maxEntries
+	m.entries[j] = e
+	m.lastEntry = j
+}
+
+// direct maps a seqno to a target seqno.  It returns true if the seqno
+// could be mapped, the target seqno, and the pid delta to apply.
+// Called with the m.mu taken.
+func (m *Map) direct(seqno uint16) (bool, uint16, uint16) {
+	if len(m.entries) == 0 {
+		return false, 0, 0
+	}
+	i := m.lastEntry
+	for {
+		f := m.entries[i].first
+		if seqno >= f {
+			if seqno < f+m.entries[i].count {
+				return true,
+					seqno + m.entries[i].delta,
+					m.entries[i].pidDelta
+			}
+			return false, 0, 0
+		}
+		if i > 0 {
+			i--
+		} else {
+			i = uint16(len(m.entries) - 1)
+		}
+		if i == m.lastEntry {
+			break
+		}
+	}
+	return false, 0, 0
+}
+
+// Reverse maps a target seqno to the original seqno.  It returns true if
+// the seqno could be mapped, the original seqno, and the pid delta to
+// apply in reverse.
+func (m *Map) Reverse(seqno uint16) (bool, uint16, uint16) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.delta == 0 && m.entries == nil {
+		return true, seqno, 0
+	}
+	if m.entries == nil {
+		if m.delta == 0 {
+			return true, seqno, 0
+		}
+		return false, 0, 0
+	}
+
+	i := m.lastEntry
+	for {
+		f := m.entries[i].first + m.entries[i].delta
+		if seqno >= f {
+			if seqno < f+m.entries[i].count {
+				return true,
+					seqno - m.entries[i].delta,
+					m.entries[i].pidDelta
+			}
+			return false, 0, 0
+		}
+		if i > 0 {
+			i--
+		} else {
+			i = uint16(len(m.entries) - 1)
+		}
+		if i == m.lastEntry {
+			break
+		}
+	}
+	return false, 0, 0
+}
+
+// Drop attempts to record a dropped packet.  It returns true if the
+// packet is safe to drop.
+func (m *Map) Drop(seqno uint16, pid uint16) bool {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if seqno != m.next {
+		return false
+	}
+
+	m.pidDelta += pid - m.nextPid
+	m.nextPid = pid
+
+	m.delta--
+	m.next = seqno + 1
+	return true
+}
+
+// compare performs comparison modulo 2^16.
+func compare(s1, s2 uint16) int {
+	if s1 == s2 {
+		return 0
+	}
+	if ((s2 - s1) & 0x8000) != 0 {
+		return 1
+	}
+	return -1
+}

packetmap/packetmap_test.go

+package packetmap
+
+import (
+	"testing"
+)
+
+func TestNoDrops(t *testing.T) {
+	m := Map{}
+
+	ok, s, p := m.Map(42, 1001)
+	if !ok || s != 42 || p != 0 {
+		t.Errorf("Expected 42, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(43, 1001)
+	if !ok || s != 43 || p != 0 {
+		t.Errorf("Expected 43, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(44, 1002)
+	if !ok || s != 44 || p != 0 {
+		t.Errorf("Expected 43, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(40, 1000)
+	if !ok || s != 40 || p != 0 {
+		t.Errorf("Expected 40, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	if len(m.entries) > 0 || m.delta != 0 || m.pidDelta != 0 {
+		t.Errorf("Expected 0, got %v %v %v",
+			len(m.entries), m.delta, m.pidDelta)
+	}
+}
+
+func TestDrop(t *testing.T) {
+	m := Map{}
+
+	ok, s, p := m.Map(42, 1001)
+	if !ok || s != 42 || p != 0 {
+		t.Errorf("Expected 42, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok = m.Drop(43, 1001)
+	if !ok || m.pidDelta != 0 {
+		t.Errorf("Expected 0, got %v, %v", ok, m.pidDelta)
+	}
+
+	ok, s, p = m.Map(44, 1001)
+	if !ok || s != 43 || p != 0 {
+		t.Errorf("Expected 43, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(45, 1002)
+	if !ok || s != 44 || p != 0 {
+		t.Errorf("Expected 44, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok = m.Drop(46, 1003)
+	if !ok || m.pidDelta != 1 {
+		t.Errorf("Expected 1, got %v, %v", ok, m.pidDelta)
+	}
+
+	ok, s, p = m.Map(47, 1003)
+	if !ok || s != 45 || p != 1 {
+		t.Errorf("Expected 45, 1, got %v, %v, %v", ok, s, p)
+	}
+
+	ok = m.Drop(48, 1003)
+	if !ok || m.pidDelta != 1 {
+		t.Errorf("Expected 1, got %v, %v", ok, m.pidDelta)
+	}
+
+	ok, s, p = m.Map(49, 1003)
+	if !ok || s != 46 || p != 1 {
+		t.Errorf("Expected 45, 1, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(60, 1007)
+	if !ok || s != 57 || p != 1 {
+		t.Errorf("Expected 57, 1, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(13, 1000)
+	if ok {
+		t.Errorf("Expected not ok")
+	}
+
+	ok, s, p = m.Map(44, 1001)
+	if !ok || s != 43 || p != 0 {
+		t.Errorf("Expected 43, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(45, 1002)
+	if !ok || s != 44 || p != 0 {
+		t.Errorf("Expected 44, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(48, 3)
+	if ok {
+		t.Errorf("Expected not ok")
+	}
+
+	ok, s, p = m.direct(1000)
+	if ok {
+		t.Errorf("Expected not ok")
+	}
+
+	ok, s, p = m.direct(13)
+	if ok {
+		t.Errorf("Expected not ok")
+	}
+
+	ok, s, p = m.Reverse(44)
+	if !ok || s != 45 || p != 0 {
+		t.Errorf("Expected 45, 0, got %v %v %v", ok, s, p)
+	}
+}
+
+func TestWraparound(t *testing.T) {
+	m := Map{}
+
+	ok, s, p := m.Map(0, 0)
+	if !ok || s != 0 || p != 0 {
+		t.Errorf("Expected 0, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(1, 0)
+	if !ok || s != 1 || p != 0 {
+		t.Errorf("Expected 1, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok = m.Drop(2, 1)
+	if !ok || m.pidDelta != 1 {
+		t.Errorf("Expected 1, got %v, %v", ok, m.pidDelta)
+	}
+
+	ok = m.Drop(3, 1)
+	if !ok || m.pidDelta != 1 {
+		t.Errorf("Expected 1, got %v, %v", ok, m.pidDelta)
+	}
+
+	for i := 4; i < 256000; i++ {
+		ok, s, p = m.Map(uint16(i), uint16((i/2) & 0x7FFF))
+		if !ok || s != uint16(i-2) || p != 1 {
+			t.Errorf("Expected %v, %v, got %v, %v, %v",
+				uint16(i-2), 1, ok, s, p)
+		}
+	}
+}
+
+func TestReset(t *testing.T) {
+	m := Map{}
+
+	ok, s, p := m.Map(42, 1001)
+	if !ok || s != 42 || p != 0 {
+		t.Errorf("Expected 42, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok = m.Drop(43, 1001)
+	if !ok || m.pidDelta != 0 {
+		t.Errorf("Expected 0, got %v, %v", ok, m.pidDelta)
+	}
+
+	ok, s, p = m.Map(44, 1001)
+	if !ok || s != 43 || p != 0 {
+		t.Errorf("Expected 43, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	ok, s, p = m.Map(40000, 2001)
+	if !ok || s != 40000 || p != 0 {
+		t.Errorf("Expected 32000, 0, got %v, %v, %v", ok, s, p)
+	}
+
+	if m.delta != 0 || m.entries != nil {
+		t.Errorf("Expected reset")
+	}
+
+	ok, s, p = m.Map(40001, 2001)
+	if !ok || s != 40001 || p != 0 {
+		t.Errorf("Expected 32001, 0, got %v, %v, %v", ok, s, p)
+	}
+}

rtpconn/codec.go

 package rtpconn
 
 import (
+	"errors"
 	"strings"
 
 	"github.com/pion/rtp"
@@ -108,3 +109,101 @@ func isKeyframe(codec string, packet *rtp.Packet) (bool, bool) {
 		return false, false
 	}
 }
+
+var errTruncated = errors.New("truncated packet")
+var errUnsupportedCodec = errors.New("unsupported codec")
+
+func packetFlags(codec string, buf []byte) (seqno uint16, start bool, pid uint16, tid uint8, sid uint8, layersync bool, discardable bool, err error) {
+	if len(buf) < 12 {
+		err = errTruncated
+		return
+	}
+
+	seqno = (uint16(buf[2]) << 8) | uint16(buf[3])
+
+	if strings.EqualFold(codec, "video/vp8") {
+		var packet rtp.Packet
+		err = packet.Unmarshal(buf)
+		if err != nil {
+			return
+		}
+		var vp8 codecs.VP8Packet
+		_, err = vp8.Unmarshal(packet.Payload)
+		if err != nil {
+			return
+		}
+
+		start = vp8.S == 1 && vp8.PID == 0
+		pid = vp8.PictureID
+		tid = vp8.TID
+		layersync = vp8.Y == 1
+		discardable = vp8.N == 1
+		return
+	} else if strings.EqualFold(codec, "video/vp9") {
+		var packet rtp.Packet
+		err = packet.Unmarshal(buf)
+		if err != nil {
+			return
+		}
+		var vp9 codecs.VP9Packet
+		_, err = vp9.Unmarshal(packet.Payload)
+		if err != nil {
+			return
+		}
+		start = vp9.B
+		tid = vp9.TID
+		sid = vp9.SID
+		layersync = vp9.U
+		return
+	}
+	return
+}
+
+func rewritePacket(codec string, data []byte, seqno uint16, delta uint16) error {
+	if len(data) < 12 {
+		return errTruncated
+	}
+
+	data[2] = uint8(seqno >> 8)
+	data[3] = uint8(seqno)
+	if delta == 0 {
+		return nil
+	}
+
+	offset := 12
+	offset += int(data[0]&0x0F) * 4
+	if len(data) < offset+4 {
+		return errTruncated
+	}
+
+	if (data[0] & 0x10) != 0 {
+		length := uint16(data[offset+2])<<8 | uint16(data[offset+3])
+		offset += 4 + int(length)*4
+		if len(data) < offset+4 {
+			return errTruncated
+		}
+	}
+
+	if strings.EqualFold(codec, "video/vp8") {
+		x := (data[offset] & 0x80) != 0
+		if !x {
+			return nil
+		}
+		i := (data[offset+1] & 0x80) != 0
+		if !i {
+			return nil
+		}
+		m := (data[offset+2] & 0x80) != 0
+		if m {
+			pid := (uint16(data[offset+2]&0x7F) << 8) |
+				uint16(data[offset+3])
+			pid = (pid + delta) & 0x7FFF
+			data[offset+2] = 0x80 | byte((pid>>8)&0x7F)
+			data[offset+3] = byte(pid & 0xFF)
+		} else {
+			data[offset+2] = (data[offset+2] + uint8(delta)) & 0x7F
+		}
+		return nil
+	}
+	return errUnsupportedCodec
+}

rtpconn/rtpconn.go

@@ -20,6 +20,7 @@ import (
 	"github.com/jech/galene/ice"
 	"github.com/jech/galene/jitter"
 	"github.com/jech/galene/packetcache"
+	"github.com/jech/galene/packetmap"
 	"github.com/jech/galene/rtptime"
 )
 
@@ -74,6 +75,7 @@ type downTrackAtomics struct {
 	srNTP     uint64
 	remoteNTP uint64
 	remoteRTP uint32
+	layerInfo uint32
 }
 
 type rtpDownTrack struct {
@@ -81,6 +83,7 @@ type rtpDownTrack struct {
 	sender         *webrtc.RTPSender
 	remote         conn.UpTrack
 	ssrc           webrtc.SSRC
+	packetmap      packetmap.Map
 	maxBitrate     *bitrate
 	maxREMBBitrate *bitrate
 	rate           *estimator.Estimator
@@ -89,14 +92,6 @@ type rtpDownTrack struct {
 	cname          atomic.Value
 }
 
-func (down *rtpDownTrack) Write(buf []byte) (int, error) {
-	n, err := down.track.Write(buf)
-	if err == nil {
-		down.rate.Accumulate(uint32(n))
-	}
-	return n, err
-}
-
 func (down *rtpDownTrack) SetTimeOffset(ntp uint64, rtp uint32) {
 	atomic.StoreUint64(&down.atomics.remoteNTP, ntp)
 	atomic.StoreUint32(&down.atomics.remoteRTP, rtp)
@@ -131,6 +126,17 @@ func (down *rtpDownTrack) SetCname(cname string) {
 	down.cname.Store(cname)
 }
 
+func (down *rtpDownTrack) getLayerInfo() (uint8, uint8, uint8) {
+	info := atomic.LoadUint32(&down.atomics.layerInfo)
+	return uint8(info >> 16), uint8(info >> 8), uint8(info)
+}
+
+func (down *rtpDownTrack) setLayerInfo(layer, wanted, max uint8) {
+	atomic.StoreUint32(&down.atomics.layerInfo,
+		(uint32(layer)<<16)|(uint32(wanted)<<8)|uint32(max),
+	)
+}
+
 const (
 	negotiationUnneeded = iota
 	negotiationNeeded
@@ -179,17 +185,108 @@ func newDownConn(c group.Client, id string, remote conn.Up) (*rtpDownConnection,
 	return conn, nil
 }
 
-func (t *rtpDownTrack) GetMaxBitrate() uint64 {
+var packetBufPool = sync.Pool{
+	New: func() interface{} {
+		return make([]byte, packetcache.BufSize)
+	},
+}
+
+func (down *rtpDownTrack) Write(buf []byte) (int, error) {
+	codec := down.remote.Codec().MimeType
+
+	seqno, start, pid, tid, _, u, _, err := packetFlags(codec, buf)
+	if err != nil {
+		return 0, err
+	}
+
+	layer, wantedLayer, maxLayer := down.getLayerInfo()
+
+	if tid > maxLayer {
+		if layer == maxLayer {
+			wantedLayer = tid
+			layer = tid
+		}
+		maxLayer = tid
+		if wantedLayer > maxLayer {
+			wantedLayer = maxLayer
+		}
+		down.setLayerInfo(layer, wantedLayer, maxLayer)
+		down.adjustLayer()
+	}
+	if start && layer != wantedLayer {
+		if u || wantedLayer < layer {
+			layer = wantedLayer
+			down.setLayerInfo(layer, wantedLayer, maxLayer)
+		}
+	}
+
+	if tid > layer {
+		ok := down.packetmap.Drop(seqno, pid)
+		if ok {
+			return 0, nil
+		}
+	}
+
+	ok, newseqno, piddelta := down.packetmap.Map(seqno, pid)
+	if !ok {
+		return 0, nil
+	}
+
+	if newseqno == seqno && piddelta == 0 {
+		return down.write(buf)
+	}
+
+	ibuf2 := packetBufPool.Get()
+	defer packetBufPool.Put(ibuf2)
+	buf2 := ibuf2.([]byte)
+
+	n := copy(buf2, buf)
+	err = rewritePacket(codec, buf2[:n], newseqno, piddelta)
+	if err != nil {
+		return 0, err
+	}
+	return down.write(buf2[:n])
+}
+
+func (down *rtpDownTrack) write(buf []byte) (int, error) {
+	n, err := down.track.Write(buf)
+	if err == nil {
+		down.rate.Accumulate(uint32(n))
+	}
+	return n, err
+}
+
+func (t *rtpDownTrack) GetMaxBitrate() (uint64, int) {
 	now := rtptime.Jiffies()
+	layer, _, _ := t.getLayerInfo()
 	r := t.maxBitrate.Get(now)
 	if r == ^uint64(0) {
 		r = 512 * 1024
 	}
 	rr := t.maxREMBBitrate.Get(now)
 	if rr == 0 || r < rr {
-		return r
+		return r, int(layer)
+	}
+	return rr, int(layer)
+}
+
+func (t *rtpDownTrack) adjustLayer() {
+	max, _ := t.GetMaxBitrate()
+	r, _ := t.rate.Estimate()
+	rate := uint64(r) * 8
+	if rate < max*7/8 {
+		layer, wanted, max := t.getLayerInfo()
+		if layer < max {
+			wanted = layer + 1
+			t.setLayerInfo(layer, wanted, max)
+		}
+	} else if rate > max*3/2 {
+		layer, wanted, max := t.getLayerInfo()
+		if layer > 0 {
+			wanted = layer - 1
+			t.setLayerInfo(layer, wanted, max)
+		}
 	}
-	return rr
 }
 
 func (down *rtpDownConnection) addICECandidate(candidate *webrtc.ICECandidateInit) error {
@@ -240,6 +337,7 @@ type rtpUpTrack struct {
 	srTime        uint64
 	srNTPTime     uint64
 	srRTPTime     uint32
+	maxLayer      uint8
 	local         []conn.DownTrack
 	bufferedNACKs []uint16
 }
@@ -598,7 +696,11 @@ func gotNACK(conn *rtpDownConnection, track *rtpDownTrack, p *rtcp.TransportLaye
 	var packet rtp.Packet
 	buf := make([]byte, packetcache.BufSize)
 	for _, nack := range p.Nacks {
-		nack.Range(func(seqno uint16) bool {
+		nack.Range(func(s uint16) bool {
+			ok, seqno, _ := track.packetmap.Reverse(s)
+			if !ok {
+				return true
+			}
 			l := track.remote.GetRTP(seqno, buf)
 			if l == 0 {
 				unhandled = append(unhandled, seqno)
@@ -785,28 +887,44 @@ func sendUpRTCP(up *rtpUpConnection) error {
 			continue
 		}
 		ssrcs = append(ssrcs, uint32(t.track.SSRC()))
-		var r uint64
 		if t.Kind() == webrtc.RTPCodecTypeAudio {
-			r = 100 * 1024
+			rate += 100 * 1024
 		} else if t.Label() == "l" {
-			r = group.LowBitrate
+			rate += group.LowBitrate
 		} else {
+			minrate := ^uint64(0)
+			maxrate := uint64(group.MinBitrate)
+			maxlayer := 0
 			local := t.getLocal()
-			r = ^uint64(0)
 			for _, down := range local {
-				rr := down.GetMaxBitrate()
-				if rr < group.MinBitrate {
-					rr = group.MinBitrate
+				r, l := down.GetMaxBitrate()
+				if maxlayer < l {
+					maxlayer = l
 				}
-				if r > rr {
-					r = rr
+				if r < group.MinBitrate {
+					r = group.MinBitrate
 				}
+				if minrate > r {
+					minrate = r
 				}
-			if r == ^uint64(0) {
-				r = 512 * 1024
+				if maxrate < r {
+					maxrate = r
+				}
+			}
+			// assume that each layer takes two times less
+			// throughput than the higher one.  Then we've
+			// got enough slack for a factor of 2^(layers-1).
+			for i := 0; i < maxlayer; i++ {
+				if minrate < ^uint64(0)/2 {
+					minrate *= 2
+				}
+			}
+			if minrate < maxrate {
+				rate += minrate
+			} else {
+				rate += maxrate
 			}
 		}
-		rate += r
 	}
 
 	if rate < ^uint64(0) && len(ssrcs) > 0 {
@@ -968,6 +1086,7 @@ func rtcpDownListener(conn *rtpDownConnection, track *rtpDownTrack, s *webrtc.RT
 			continue
 		}
 
+		adjust := false
 		jiffies := rtptime.Jiffies()
 
 		for _, p := range ps {
@@ -994,10 +1113,12 @@ func rtcpDownListener(conn *rtpDownConnection, track *rtpDownTrack, s *webrtc.RT
 				}
 			case *rtcp.ReceiverEstimatedMaximumBitrate:
 				track.maxREMBBitrate.Set(p.Bitrate, jiffies)
+				adjust = true
 			case *rtcp.ReceiverReport:
 				for _, r := range p.Reports {
 					if r.SSRC == uint32(track.ssrc) {
 						handleReport(track, r, jiffies)
+						adjust = true
 					}
 				}
 			case *rtcp.SenderReport:
@@ -1010,6 +1131,9 @@ func rtcpDownListener(conn *rtpDownConnection, track *rtpDownTrack, s *webrtc.RT
 				gotNACK(conn, track, p)
 			}
 		}
+		if adjust {
+			track.adjustLayer()
+		}
 	}
 }
 

rtpconn/rtpstats.go

@@ -49,6 +49,8 @@ func (c *webClient) GetStats() *stats.Client {
 			Id: down.id,
 		}
 		for _, t := range down.tracks {
+			l, _, _ := t.getLayerInfo()
+			layer := int(l)
 			rate, _ := t.rate.Estimate()
 			rtt := rtptime.ToDuration(t.getRTT(),
 				rtptime.JiffiesPerSec)
@@ -56,6 +58,7 @@ func (c *webClient) GetStats() *stats.Client {
 			j := time.Duration(jitter) * time.Second /
 				time.Duration(t.track.Codec().ClockRate)
 			conns.Tracks = append(conns.Tracks, stats.Track{
+				Layer:      &layer,
 				Bitrate:    uint64(rate) * 8,
 				MaxBitrate: t.maxBitrate.Get(jiffies),
 				Loss:       float64(loss) / 256.0,

rtpconn/webclient.go

@@ -1270,6 +1270,9 @@ func handleClientMessage(c *webClient, m clientMessage) error {
 			return closeDownConn(c, m.Id, message)
 		}
 		down := getDownConn(c, m.Id)
+		if down == nil {
+			return ErrUnknownId
+		}
 		if down.negotiationNeeded > negotiationUnneeded {
 			err := negotiate(
 				c, down,

static/stats.js

@@ -95,23 +95,26 @@ function formatTrack(table, track) {
     tr.appendChild(document.createElement('td'));
     tr.appendChild(document.createElement('td'));
     let td = document.createElement('td');
-    if(track.maxBitrate)
-        td.textContent = `${track.bitrate||0}/${track.maxBitrate}`;
-    else
-        td.textContent = `${track.bitrate||0}`;
+    td.textContent = track.layer;
     tr.appendChild(td);
     let td2 = document.createElement('td');
-    td2.textContent = `${Math.round(track.loss * 100)}%`;
+    if(track.maxBitrate)
+        td2.textContent = `${track.bitrate||0}/${track.maxBitrate}`;
+    else
+        td2.textContent = `${track.bitrate||0}`;
     tr.appendChild(td2);
     let td3 = document.createElement('td');
+    td3.textContent = `${Math.round(track.loss * 100)}%`;
+    tr.appendChild(td3);
+    let td4 = document.createElement('td');
     let text = '';
     if(track.rtt) {
         text = text + `${Math.round(track.rtt * 1000) / 1000}ms`;
     }
     if(track.jitter)
         text = text + `±${Math.round(track.jitter * 1000) / 1000}ms`;
-    td3.textContent = text;
-    tr.appendChild(td3);
+    td4.textContent = text;
+    tr.appendChild(td4);
     table.appendChild(tr);
 }
 

stats/stats.go

@@ -47,6 +47,7 @@ func (d *Duration) UnmarshalJSON(buf []byte) error {
 }
 
 type Track struct {
+	Layer      *int     `json:"layer,omitempty"`
 	Bitrate    uint64   `json:"bitrate"`
 	MaxBitrate uint64   `json:"maxBitrate,omitempty"`
 	Loss       float64  `json:"loss"`