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reorderer.go
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reorderer.go
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package rtpreorderer
import (
"github.com/pion/rtp"
)
const (
bufferSize = 64
)
// Reorderer filters incoming RTP packets, in order to
// - order packets
// - remove duplicate packets
type Reorderer struct {
initialized bool
expectedSeqNum uint16
buffer []*rtp.Packet
absPos uint16
}
// New allocates a Reorderer.
func New() *Reorderer {
return &Reorderer{
buffer: make([]*rtp.Packet, bufferSize),
}
}
// Process processes a RTP packet.
func (r *Reorderer) Process(pkt *rtp.Packet) []*rtp.Packet {
if !r.initialized {
r.initialized = true
r.expectedSeqNum = pkt.SequenceNumber + 1
return []*rtp.Packet{pkt}
}
relPos := pkt.SequenceNumber - r.expectedSeqNum
// packet is a duplicate or has been sent
// before the first packet processed by Reorderer.
// discard.
if relPos > 0xFFF {
return nil
}
// there's a missing packet and buffer is full.
// return entire buffer and clear it.
if relPos >= bufferSize {
n := 1
for i := uint16(0); i < bufferSize; i++ {
p := (r.absPos + i) & (bufferSize - 1)
if r.buffer[p] != nil {
n++
}
}
ret := make([]*rtp.Packet, n)
pos := 0
for i := uint16(0); i < bufferSize; i++ {
p := (r.absPos + i) & (bufferSize - 1)
if r.buffer[p] != nil {
ret[pos] = r.buffer[p]
pos++
}
}
ret[pos] = pkt
for i := 0; i < bufferSize; i++ {
r.buffer[i] = nil
}
r.expectedSeqNum = pkt.SequenceNumber + 1
return ret
}
// there's a missing packet
if relPos != 0 {
p := (r.absPos + relPos) & (bufferSize - 1)
// current packet is a duplicate. discard
if r.buffer[p] != nil {
return nil
}
// put current packet in buffer
r.buffer[p] = pkt
return nil
}
// all packets have been received correctly.
// return them
n := uint16(1)
for {
p := (r.absPos + n) & (bufferSize - 1)
if r.buffer[p] == nil {
break
}
n++
}
ret := make([]*rtp.Packet, n)
ret[0] = pkt
r.absPos++
r.absPos &= (bufferSize - 1)
for i := uint16(1); i < n; i++ {
ret[i], r.buffer[r.absPos] = r.buffer[r.absPos], nil
r.absPos++
r.absPos &= (bufferSize - 1)
}
r.expectedSeqNum = pkt.SequenceNumber + n
return ret
}