From 5cc35a77a5d447a2015dccec5f9968feedfdbcb0 Mon Sep 17 00:00:00 2001
From: saxon <saxon.milton@gmail.com>
Date: Sat, 17 Nov 2018 23:17:08 +1030
Subject: [PATCH] rtp: finished encoder file - wrote encode function, wrote
 timestamp function and sequence number function - need to test

---
 stream/rtp/encoder.go | 65 +++++++++++++++++++++----------------------
 stream/rtp/rtp.go     |  6 ++--
 2 files changed, 35 insertions(+), 36 deletions(-)

diff --git a/stream/rtp/encoder.go b/stream/rtp/encoder.go
index ada69395..315f66e8 100644
--- a/stream/rtp/encoder.go
+++ b/stream/rtp/encoder.go
@@ -29,51 +29,52 @@ package rtp
 
 import (
 	"io"
+	"math/rand"
 	"time"
 )
 
-// Time related constants.
 const (
-	rtpVer  = 2
-	yes     = 1
-	no      = 0
-	ccCount = 0
-	// pcrFreq is the base Program Clock Reference frequency.
-	timestampFreq = 90000 // Hz
+	yes            = 1
+	no             = 0
+	defaultPktType = 1
+	timestampFreq  = 90000 // Hz
 )
 
 type Encoder struct {
-	dst io.Writer
-
+	dst           io.Writer
+	ssrc          uint32
+	seqNo         uint16
 	clock         time.Duration
 	frameInterval time.Duration
 }
 
-// NewEncoder returns an Encoder with the specified frame rate.
+// NewEncoder returns a new Encoder type given an io.Writer - the destination
+// after encoding and the desired fps
 func NewEncoder(dst io.Writer, fps float64) *Encoder {
 	return &Encoder{
 		dst:           dst,
+		ssrc:          rand.Uint32(),
 		frameInterval: time.Duration(float64(time.Second) / fps),
 	}
 }
 
+// Encode takes a nalu unit and encodes it into an rtp packet and
+// writes to the io.Writer given in NewEncoder
 func (e *Encoder) Encode(nalu []byte) error {
 	pkt := Pkt{
-		Pkt{
-			V:       rtpVer, // version
-			P:       no,     // padding
-			X:       no,     // header extension
-			CC:      ccCount,
-			M:       no, // NOTE: need to check if this works (decoders should ignore this)
-			PT:      6,
-			SN:      167,
-			TS:      160,
-			SSRC:    10,
-			Payload: []byte{0x00, 0x01, 0x07, 0xf0, 0x56, 0x37, 0x0a, 0x0f},
-			Padding: 0,
-		},
+		V:       rtpVer,           // version
+		P:       no,               // padding
+		X:       no,               // header extension
+		CC:      no,               // CSRC count
+		M:       no,               // NOTE: need to check if this works (decoders should ignore this)
+		PT:      defaultPktType,   // NOTE: 1-23 according to rtp-h264 specs (don't think we need this)
+		SN:      e.nxtSeqNo(),     // sequence number
+		TS:      e.nxtTimestamp(), // timestamp
+		SSRC:    e.ssrc,           // source identifier
+		Payload: nalu,
+		Padding: no,
 	}
-	// Write rtp packet to
+
 	_, err := e.dst.Write(pkt.Bytes())
 	if err != nil {
 		return err
@@ -89,15 +90,13 @@ func (e *Encoder) tick() {
 	e.clock += e.frameInterval
 }
 
-// TODO: alter and make this work for rtp
-func (e *Encoder) pts() uint64 {
-	return uint64((e.clock + e.ptsOffset).Seconds() * pcrFreq)
+// nxtTimestamp gets the next timestamp
+func (e *Encoder) nxtTimestamp() uint32 {
+	return uint32(e.clock.Seconds() * timestampFreq)
 }
 
-// TODO: alter and apply this to rtp for sequence number
-func (e *Encoder) ccFor(pid int) byte {
-	cc := e.continuity[pid]
-	const continuityCounterMask = 0xf
-	e.continuity[pid] = (cc + 1) & continuityCounterMask
-	return cc
+// nxtSeqNo gets the next rtp packet sequence number
+func (e *Encoder) nxtSeqNo() uint16 {
+	e.seqNo += 1
+	return e.seqNo - 1
 }
diff --git a/stream/rtp/rtp.go b/stream/rtp/rtp.go
index bdf81e93..e4f36218 100644
--- a/stream/rtp/rtp.go
+++ b/stream/rtp/rtp.go
@@ -41,9 +41,9 @@ type Pkt struct {
 	CC      byte   // CSRC count
 	M       byte   // Marker bit
 	PT      byte   // Packet type
-	SN      int16  // Synch number
-	TS      int32  // Timestamp
-	SSRC    int32  // Synchronisation source identifier
+	SN      uint16 // Synch number
+	TS      uint32 // Timestamp
+	SSRC    uint32 // Synchronisation source identifier
 	Payload []byte // H264 Payload data
 	Padding int    // No of bytes of padding
 }