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package rtp
import (
"time"
)
// Payloader payloads a byte array for use as rtp.Packet payloads
type Payloader interface {
Payload(mtu int, payload []byte) [][]byte
}
// Packetizer packetizes a payload
type Packetizer interface {
Packetize(payload []byte, samples uint32) []*Packet
EnableAbsSendTime(value int)
}
type packetizer struct {
MTU int
PayloadType uint8
SSRC uint32
Payloader Payloader
Sequencer Sequencer
Timestamp uint32
ClockRate uint32
extensionNumbers struct { // put extension numbers in here. If they're 0, the extension is disabled (0 is not a legal extension number)
AbsSendTime int // http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
}
timegen func() time.Time
}
// NewPacketizer returns a new instance of a Packetizer for a specific payloader
func NewPacketizer(mtu int, pt uint8, ssrc uint32, payloader Payloader, sequencer Sequencer, clockRate uint32) Packetizer {
return &packetizer{
MTU: mtu,
PayloadType: pt,
SSRC: ssrc,
Payloader: payloader,
Sequencer: sequencer,
Timestamp: globalMathRandomGenerator.Uint32(),
ClockRate: clockRate,
timegen: time.Now,
}
}
func (p *packetizer) EnableAbsSendTime(value int) {
p.extensionNumbers.AbsSendTime = value
}
// Packetize packetizes the payload of an RTP packet and returns one or more RTP packets
func (p *packetizer) Packetize(payload []byte, samples uint32) []*Packet {
// Guard against an empty payload
if len(payload) == 0 {
return nil
}
payloads := p.Payloader.Payload(p.MTU-12, payload)
packets := make([]*Packet, len(payloads))
for i, pp := range payloads {
packets[i] = &Packet{
Header: Header{
Version: 2,
Padding: false,
Extension: false,
Marker: i == len(payloads)-1,
PayloadType: p.PayloadType,
SequenceNumber: p.Sequencer.NextSequenceNumber(),
Timestamp: p.Timestamp, // Figure out how to do timestamps
SSRC: p.SSRC,
},
Payload: pp,
}
}
p.Timestamp += samples
if len(packets) != 0 && p.extensionNumbers.AbsSendTime != 0 {
sendTime := NewAbsSendTimeExtension(p.timegen())
// apply http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
b, err := sendTime.Marshal()
if err != nil {
return nil // never happens
}
err = packets[len(packets)-1].SetExtension(uint8(p.extensionNumbers.AbsSendTime), b)
if err != nil {
return nil // never happens
}
}
return packets
}
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