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rtpmunger.go
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rtpmunger.go
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package sfu
import (
"fmt"
"github.com/abdulhaseeb08/protocol/logger"
"github.com/abdulhaseeb08/livekit-server/pkg/sfu/buffer"
)
//
// RTPMunger
//
type SequenceNumberOrdering int
const (
SequenceNumberOrderingContiguous SequenceNumberOrdering = iota
SequenceNumberOrderingOutOfOrder
SequenceNumberOrderingGap
SequenceNumberOrderingDuplicate
)
const (
RtxGateWindow = 2000
SnOffsetCacheSize = 4096
SnOffsetCacheMask = SnOffsetCacheSize - 1
)
type TranslationParamsRTP struct {
snOrdering SequenceNumberOrdering
sequenceNumber uint16
timestamp uint32
}
type SnTs struct {
sequenceNumber uint16
timestamp uint32
}
// ----------------------------------------------------------------------
type RTPMungerState struct {
LastSN uint16
LastTS uint32
}
func (r RTPMungerState) String() string {
return fmt.Sprintf("RTPMungerState{lastSN: %d, lastTS: %d)", r.LastSN, r.LastTS)
}
// ----------------------------------------------------------------------
type RTPMungerParams struct {
highestIncomingSN uint16
lastSN uint16
snOffset uint16
lastTS uint32
tsOffset uint32
lastMarker bool
snOffsets [SnOffsetCacheSize]uint16
snOffsetsWritePtr int
snOffsetsOccupancy int
rtxGateSn uint16
isInRtxGateRegion bool
}
type RTPMunger struct {
logger logger.Logger
RTPMungerParams
}
func NewRTPMunger(logger logger.Logger) *RTPMunger {
return &RTPMunger{
logger: logger,
}
}
func (r *RTPMunger) GetParams() RTPMungerParams {
return RTPMungerParams{
highestIncomingSN: r.highestIncomingSN,
lastSN: r.lastSN,
snOffset: r.snOffset,
lastTS: r.lastTS,
tsOffset: r.tsOffset,
lastMarker: r.lastMarker,
}
}
func (r *RTPMunger) GetLast() RTPMungerState {
return RTPMungerState{
LastSN: r.lastSN,
LastTS: r.lastTS,
}
}
func (r *RTPMunger) SeedLast(state RTPMungerState) {
r.lastSN = state.LastSN
r.lastTS = state.LastTS
}
func (r *RTPMunger) SetLastSnTs(extPkt *buffer.ExtPacket) {
r.highestIncomingSN = extPkt.Packet.SequenceNumber - 1
r.lastSN = extPkt.Packet.SequenceNumber
r.lastTS = extPkt.Packet.Timestamp
}
func (r *RTPMunger) UpdateSnTsOffsets(extPkt *buffer.ExtPacket, snAdjust uint16, tsAdjust uint32) {
r.highestIncomingSN = extPkt.Packet.SequenceNumber - 1
r.snOffset = extPkt.Packet.SequenceNumber - r.lastSN - snAdjust
r.tsOffset = extPkt.Packet.Timestamp - r.lastTS - tsAdjust
// clear offsets cache layer/source switch
r.snOffsetsWritePtr = 0
r.snOffsetsOccupancy = 0
}
func (r *RTPMunger) PacketDropped(extPkt *buffer.ExtPacket) {
if r.highestIncomingSN != extPkt.Packet.SequenceNumber {
return
}
r.snOffset += 1
r.lastSN = extPkt.Packet.SequenceNumber - r.snOffset
r.snOffsetsWritePtr = (r.snOffsetsWritePtr - 1) & SnOffsetCacheMask
r.snOffsetsOccupancy--
if r.snOffsetsOccupancy < 0 {
r.logger.Warnw("sequence number offset cache is invalid", nil, "occupancy", r.snOffsetsOccupancy)
}
}
func (r *RTPMunger) UpdateAndGetSnTs(extPkt *buffer.ExtPacket) (*TranslationParamsRTP, error) {
// if out-of-order, look up sequence number offset cache
diff := extPkt.Packet.SequenceNumber - r.highestIncomingSN
if diff > (1 << 15) {
snOffset, isValid := r.getSnOffset(extPkt.Packet.SequenceNumber)
if !isValid {
return &TranslationParamsRTP{
snOrdering: SequenceNumberOrderingOutOfOrder,
}, ErrOutOfOrderSequenceNumberCacheMiss
}
return &TranslationParamsRTP{
snOrdering: SequenceNumberOrderingOutOfOrder,
sequenceNumber: extPkt.Packet.SequenceNumber - snOffset,
timestamp: extPkt.Packet.Timestamp - r.tsOffset,
}, nil
}
// record sn offset
for i := r.highestIncomingSN + 1; i != extPkt.Packet.SequenceNumber+1; i++ {
r.snOffsets[r.snOffsetsWritePtr] = r.snOffset
r.snOffsetsWritePtr = (r.snOffsetsWritePtr + 1) & SnOffsetCacheMask
r.snOffsetsOccupancy++
}
if r.snOffsetsOccupancy > SnOffsetCacheSize {
r.snOffsetsOccupancy = SnOffsetCacheSize
}
ordering := SequenceNumberOrderingContiguous
if diff > 1 {
ordering = SequenceNumberOrderingGap
} else {
// can get duplicate packet due to FEC
if diff == 0 {
return &TranslationParamsRTP{
snOrdering: SequenceNumberOrderingDuplicate,
}, ErrDuplicatePacket
}
// if padding only packet, can be dropped and sequence number adjusted
// as it is contiguous and in order. That means this is the highest
// incoming sequence number, and it is a good point to adjust
// sequence number offset.
if len(extPkt.Packet.Payload) == 0 {
r.highestIncomingSN = extPkt.Packet.SequenceNumber
r.snOffset += 1
return &TranslationParamsRTP{
snOrdering: SequenceNumberOrderingContiguous,
}, ErrPaddingOnlyPacket
}
}
// in-order incoming packet, may or may not be contiguous.
// In the case of loss (i.e. incoming sequence number is not contiguous),
// forward even if it is a padding only packet. With temporal scalability,
// it is unclear if the current packet should be dropped if it is not
// contiguous. Hence, forward anything that is not contiguous.
// Reference: http://www.rtcbits.com/2017/04/howto-implement-temporal-scalability.html
mungedSN := extPkt.Packet.SequenceNumber - r.snOffset
mungedTS := extPkt.Packet.Timestamp - r.tsOffset
r.highestIncomingSN = extPkt.Packet.SequenceNumber
r.lastSN = mungedSN
r.lastTS = mungedTS
r.lastMarker = extPkt.Packet.Marker
if extPkt.KeyFrame {
r.rtxGateSn = mungedSN
r.isInRtxGateRegion = true
}
if r.isInRtxGateRegion && (mungedSN-r.rtxGateSn) > RtxGateWindow {
r.isInRtxGateRegion = false
}
return &TranslationParamsRTP{
snOrdering: ordering,
sequenceNumber: mungedSN,
timestamp: mungedTS,
}, nil
}
func (r *RTPMunger) FilterRTX(nacks []uint16) []uint16 {
if !r.isInRtxGateRegion {
return nacks
}
filtered := make([]uint16, 0, len(nacks))
for _, sn := range nacks {
if (sn - r.rtxGateSn) < (1 << 15) {
filtered = append(filtered, sn)
}
}
return filtered
}
func (r *RTPMunger) UpdateAndGetPaddingSnTs(num int, clockRate uint32, frameRate uint32, forceMarker bool) ([]SnTs, error) {
tsOffset := 0
if !r.lastMarker {
if !forceMarker {
return nil, ErrPaddingNotOnFrameBoundary
} else {
// if forcing frame end, use timestamp of latest received frame for the first one
tsOffset = 1
}
}
vals := make([]SnTs, num)
for i := 0; i < num; i++ {
vals[i].sequenceNumber = r.lastSN + uint16(i) + 1
if frameRate != 0 {
vals[i].timestamp = r.lastTS + uint32(i+1-tsOffset)*(clockRate/frameRate)
} else {
vals[i].timestamp = r.lastTS
}
}
r.lastSN = vals[num-1].sequenceNumber
r.snOffset -= uint16(num)
r.tsOffset -= vals[num-1].timestamp - r.lastTS
r.lastTS = vals[num-1].timestamp
if forceMarker {
r.lastMarker = true
}
return vals, nil
}
func (r *RTPMunger) IsOnFrameBoundary() bool {
return r.lastMarker
}
func (r *RTPMunger) getSnOffset(sn uint16) (uint16, bool) {
diff := r.highestIncomingSN - sn
if int(diff) >= r.snOffsetsOccupancy {
return 0, false
}
readPtr := (r.snOffsetsWritePtr - int(diff) - 1) & SnOffsetCacheMask
return r.snOffsets[readPtr], true
}