Files
gortsplib/pkg/format/rtpmpeg1video/encoder.go
2023-09-19 22:15:39 +02:00

240 lines
4.7 KiB
Go

package rtpmpeg1video
import (
"bytes"
"crypto/rand"
"github.com/pion/rtp"
)
const (
rtpVersion = 2
defaultPayloadMaxSize = 1460 // 1500 (UDP MTU) - 20 (IP header) - 8 (UDP header) - 12 (RTP header)
)
func randUint32() (uint32, error) {
var b [4]byte
_, err := rand.Read(b[:])
if err != nil {
return 0, err
}
return uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3]), nil
}
func lenAggregated(slices [][]byte, slice []byte) int {
n := 4 + len(slice)
for _, fr := range slices {
n += len(fr)
}
return n
}
func packetCount(avail, le int) int {
n := le / avail
if (le % avail) != 0 {
n++
}
return n
}
// Encoder is a RTP/MPEG-1/2 Video encoder.
// Specification: https://datatracker.ietf.org/doc/html/rfc2250
type Encoder struct {
// SSRC of packets (optional).
// It defaults to a random value.
SSRC *uint32
// initial sequence number of packets (optional).
// It defaults to a random value.
InitialSequenceNumber *uint16
// maximum size of packet payloads (optional).
// It defaults to 1460.
PayloadMaxSize int
sequenceNumber uint16
}
// Init initializes the encoder.
func (e *Encoder) Init() error {
if e.SSRC == nil {
v, err := randUint32()
if err != nil {
return err
}
e.SSRC = &v
}
if e.InitialSequenceNumber == nil {
v, err := randUint32()
if err != nil {
return err
}
v2 := uint16(v)
e.InitialSequenceNumber = &v2
}
if e.PayloadMaxSize == 0 {
e.PayloadMaxSize = defaultPayloadMaxSize
}
e.sequenceNumber = *e.InitialSequenceNumber
return nil
}
// Encode encodes frames into RTP packets.
func (e *Encoder) Encode(frame []byte) ([]*rtp.Packet, error) {
var rets []*rtp.Packet
var batch [][]byte
var temporalReference uint16
beginOfSequence := uint8(0)
var frameType uint8
for {
var slice []byte
end := bytes.Index(frame[4:], []byte{0, 0, 1})
if end >= 0 {
slice, frame = frame[:end+4], frame[end+4:]
} else {
slice, frame = frame, nil
}
if lenAggregated(batch, slice) <= e.PayloadMaxSize {
batch = append(batch, slice)
} else {
// write current batch
if batch != nil {
pkts, err := e.writeBatch(batch,
temporalReference,
beginOfSequence,
frameType)
if err != nil {
return nil, err
}
rets = append(rets, pkts...)
beginOfSequence = 0
}
// initialize new batch
batch = [][]byte{slice}
}
switch slice[3] {
case 0:
temporalReference = uint16(slice[4])<<2 | uint16(slice[5])>>6
frameType = (slice[5] >> 3) & 0b111
case 0xB8:
beginOfSequence = 1
}
if frame == nil {
break
}
}
// write last batch
pkts, err := e.writeBatch(batch,
temporalReference,
beginOfSequence,
frameType)
if err != nil {
return nil, err
}
rets = append(rets, pkts...)
rets[len(rets)-1].Marker = true
return rets, nil
}
func (e *Encoder) writeBatch(
slices [][]byte,
temporalReference uint16,
beginOfSequence uint8,
frameType uint8,
) ([]*rtp.Packet, error) {
if len(slices) != 1 || lenAggregated(slices, nil) < e.PayloadMaxSize {
return e.writeAggregated(slices, temporalReference, beginOfSequence, frameType)
}
return e.writeFragmented(slices[0], temporalReference, beginOfSequence, frameType)
}
func (e *Encoder) writeFragmented(
slice []byte,
temporalReference uint16,
beginOfSequence uint8,
frameType uint8,
) ([]*rtp.Packet, error) {
avail := e.PayloadMaxSize - 4
le := len(slice)
packetCount := packetCount(avail, le)
ret := make([]*rtp.Packet, packetCount)
le = avail
start := uint8(1)
end := uint8(0)
for i := range ret {
if i == (packetCount - 1) {
le = len(slice)
end = 1
}
payload := make([]byte, 4+le)
payload[0] = byte(temporalReference >> 8)
payload[1] = byte(temporalReference)
payload[2] = beginOfSequence<<5 | start<<4 | end<<3 | frameType
copy(payload[4:], slice)
slice = slice[le:]
ret[i] = &rtp.Packet{
Header: rtp.Header{
Version: rtpVersion,
PayloadType: 32,
SequenceNumber: e.sequenceNumber,
SSRC: *e.SSRC,
},
Payload: payload,
}
e.sequenceNumber++
start = 0
beginOfSequence = 0
}
return ret, nil
}
func (e *Encoder) writeAggregated(
slices [][]byte,
temporalReference uint16,
beginOfSequence uint8,
frameType uint8,
) ([]*rtp.Packet, error) {
payload := make([]byte, lenAggregated(slices, nil))
payload[0] = byte(temporalReference >> 8)
payload[1] = byte(temporalReference)
payload[2] = beginOfSequence<<5 | 1<<4 | 1<<3 | frameType
n := 4
for _, slice := range slices {
n += copy(payload[n:], slice)
}
pkt := &rtp.Packet{
Header: rtp.Header{
Version: rtpVersion,
PayloadType: 32,
SequenceNumber: e.sequenceNumber,
SSRC: *e.SSRC,
},
Payload: payload,
}
e.sequenceNumber++
return []*rtp.Packet{pkt}, nil
}