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redreceiver.go
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redreceiver.go
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// Copyright 2023 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 sfu
import (
"encoding/binary"
"fmt"
"go.uber.org/atomic"
"github.com/pion/rtp"
"github.com/livekit/livekit-server/pkg/sfu/buffer"
"github.com/livekit/mediatransportutil/pkg/bucket"
"github.com/livekit/protocol/livekit"
"github.com/livekit/protocol/logger"
)
const (
maxRedCount = 2
mtuSize = 1500
// the RedReceiver is only for chrome / native webrtc now, we always negotiate opus payload to 111 with those clients,
// so it is safe to use a fixed payload 111 here for performance(avoid encoding red blocks for each downtrack that
// have a different opus payload type).
opusPT = 111
)
type RedReceiver struct {
TrackReceiver
downTrackSpreader *DownTrackSpreader
logger logger.Logger
closed atomic.Bool
pktBuff [maxRedCount]*rtp.Packet
redPayloadBuf [mtuSize]byte
}
func NewRedReceiver(receiver TrackReceiver, dsp DownTrackSpreaderParams) *RedReceiver {
return &RedReceiver{
TrackReceiver: receiver,
downTrackSpreader: NewDownTrackSpreader(dsp),
logger: dsp.Logger,
}
}
func (r *RedReceiver) ForwardRTP(pkt *buffer.ExtPacket, spatialLayer int32) {
// extract primary payload from RED and forward to downtracks
if r.downTrackSpreader.DownTrackCount() == 0 {
return
}
redLen, err := r.encodeRedForPrimary(pkt.Packet, r.redPayloadBuf[:])
if err != nil {
r.logger.Errorw("red encoding failed", err)
return
}
pPkt := *pkt
redRtpPacket := *pkt.Packet
redRtpPacket.Payload = r.redPayloadBuf[:redLen]
pPkt.Packet = &redRtpPacket
// not modify the ExtPacket.RawPacket here for performance since it is not used by the DownTrack,
// otherwise it should be set to the correct value (marshal the primary rtp packet)
r.downTrackSpreader.Broadcast(func(dt TrackSender) {
_ = dt.WriteRTP(&pPkt, spatialLayer)
})
}
func (r *RedReceiver) AddDownTrack(track TrackSender) error {
if r.closed.Load() {
return ErrReceiverClosed
}
if r.downTrackSpreader.HasDownTrack(track.SubscriberID()) {
r.logger.Infow("subscriberID already exists, replacing downtrack", "subscriberID", track.SubscriberID())
}
track.TrackInfoAvailable()
r.downTrackSpreader.Store(track)
r.logger.Debugw("red receiver downtrack added", "subscriberID", track.SubscriberID())
return nil
}
func (r *RedReceiver) DeleteDownTrack(subscriberID livekit.ParticipantID) {
if r.closed.Load() {
return
}
r.downTrackSpreader.Free(subscriberID)
r.logger.Debugw("red receiver downtrack deleted", "subscriberID", subscriberID)
}
func (r *RedReceiver) CanClose() bool {
return r.closed.Load() || r.downTrackSpreader.DownTrackCount() == 0
}
func (r *RedReceiver) IsClosed() bool {
return r.closed.Load()
}
func (r *RedReceiver) Close() {
r.closed.Store(true)
closeTrackSenders(r.downTrackSpreader.ResetAndGetDownTracks())
}
func (r *RedReceiver) ReadRTP(buf []byte, layer uint8, sn uint16) (int, error) {
// red encoding don't support nack
return 0, bucket.ErrPacketMismatch
}
func (r *RedReceiver) encodeRedForPrimary(pkt *rtp.Packet, redPayload []byte) (int, error) {
redLength := len(r.pktBuff)
redPkts := make([]*rtp.Packet, 0, redLength+1)
lastNilPkt := -1
for i := redLength - 1; i >= 0; i-- {
if r.pktBuff[i] == nil {
lastNilPkt = i
break
}
}
for _, prev := range r.pktBuff[lastNilPkt+1:] {
if pkt.SequenceNumber == prev.SequenceNumber ||
(pkt.SequenceNumber-prev.SequenceNumber) > uint16(redLength) ||
(pkt.Timestamp-prev.Timestamp) >= (1<<14) {
continue
}
redPkts = append(redPkts, prev)
}
// insert primary packet in history buffer
// NOTE: packet is copied from retransmission buffer and used in forwarding path. So, not making another
// copy here and just maintaining pointer to the packet as the forwarding path should not alter the packet.
for i := redLength - 1; i >= 0; i-- {
if r.pktBuff[i] == nil || // history is empty
pkt.SequenceNumber-r.pktBuff[i].SequenceNumber < (1<<15) { // received packet has more recent sequence number
// age out older ones
for j := 0; j < i; j++ {
r.pktBuff[j] = r.pktBuff[j+1]
}
r.pktBuff[i] = pkt
break
}
}
return encodeRedForPrimary(redPkts, pkt, redPayload)
}
func encodeRedForPrimary(redPkts []*rtp.Packet, primary *rtp.Packet, redPayload []byte) (int, error) {
payloadSize := len(primary.Payload) + 1
for _, p := range redPkts {
payloadSize += len(p.Payload) + 4
}
// if required payload size is larger than the redPayload buffer, encode the primary packet only
if payloadSize > len(redPayload) {
redPkts = redPkts[:0]
}
var index int
for _, p := range redPkts {
/* RED payload https://datatracker.ietf.org/doc/html/rfc2198#section-3
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F| block PT | timestamp offset | block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
F: 1 bit First bit in header indicates whether another header block
follows. If 1 further header blocks follow, if 0 this is the
last header block.
*/
header := uint32(0x80 | uint8(opusPT))
header <<= 14
header |= (primary.Timestamp - p.Timestamp) & 0x3FFF
header <<= 10
header |= uint32(len(p.Payload)) & 0x3FF
binary.BigEndian.PutUint32(redPayload[index:], header)
index += 4
}
// last block header
redPayload[index] = uint8(opusPT)
index++
// append data blocks
redPkts = append(redPkts, primary)
for _, p := range redPkts {
if copy(redPayload[index:], p.Payload) < len(p.Payload) {
return 0, fmt.Errorf("red payload don't have enough space, needsize %d", len(p.Payload))
}
index += len(p.Payload)
}
return index, nil
}