/*
NAME
  revid - a testbed for re-muxing and re-directing video streams as MPEG-TS over various protocols.

DESCRIPTION
  See Readme.md

AUTHOR
  Alan Noble <anoble@gmail.com>

LICENSE
  revid is Copyright (C) 2017 Alan Noble.

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 for more details.

  You should have received a copy of the GNU General Public License
  along with revid in gpl.txt.  If not, see [GNU licenses](http://www.gnu.org/licenses).
*/

// revid is a testbed for re-muxing and re-directing video streams as MPEG-TS over various protocols.
package main

import (
	"bufio"
	"bytes"
	"crypto/md5"
	"encoding/binary"
	"encoding/hex"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"math/rand"
	"net"
	"net/http"
	"os"
	"runtime"
	"strconv"
	"strings"
	"time"
	"io"

	"../packets"

	"bitbucket.org/ausocean/av/ringbuffer"

	"github.com/Comcast/gots/packet"
	"github.com/Comcast/gots/packet/adaptationfield"
	"github.com/Comcast/gots/psi"
	"github.com/beatgammit/rtsp"
)

// defaults and networking consts
const (
	clipDuration       = 1 // s
	defaultPID         = 256
	defaultFrameRate   = 25
	defaultHTTPOutput  = "http://localhost:8080?"
	defaultUDPOutput   = "udp://0.0.0.0:16384"
	defaultRTPOutput   = "rtp://0.0.0.0:16384"
	mp2tPacketSize     = 188                 // MPEG-TS packet size
	mp2tMaxPackets     = 2016 * clipDuration // # first multiple of 7 and 8 greater than 2000
	udpPackets         = 7                   // # of UDP packets per ethernet frame (8 is the max)
	rtpPackets         = 7                   // # of RTP packets per ethernet frame (7 is the max)
	rtpHeaderSize      = 12
	rtpSSRC            = 1 // any value will do
	bufferSize         = 1000 / clipDuration
	bitrateOutputDelay = 60 // s
	httpTimeOut        = 5  // s
	motionThreshold    = "0.0025"
	qscale             = "3"
	rtpPort = 17300
  rtcpPort = 17319
  rtspUrl = "rtsp://192.168.0.50:8554/CH002.sdp"
  rtpUrl = "rtsp://192.168.0.50:8554/CH002.sdp/track1"
)

// flag values
const (
	filterFixPTS        = 0x0001
	filterDropAudio     = 0x0002
	filterScale640      = 0x0004
	filterScale320      = 0x0008
	filterFixContinuity = 0x0010
	filterEdgeDetection = 0x0020
	filterMotionDetect  = 0x0040
	filterRepacket = 0x0080
	dumpProgramInfo     = 0x0100 // 256
	dumpPacketStats     = 0x0200 // 512
	dumpPacketHeader    = 0x0400 // 1024
	dumpPacketPayload   = 0x0800 // 2048
)

// globals
var (
	sendClip        = sendClipToRTP
	packetsPerFrame = rtpPackets
	clipCount       int
	expectCC        int
	dumpCC          int
	dumpPCRBase     uint64
	rtpSequenceNum  uint16
	conn            net.Conn
	ffmpegPath      string
	tempDir         string
	inputErrChan    chan error
	outputErrChan   chan error
	ringBuffer      ringbuffer.RingBuffer
)

// command-line flags
var (
	inputURL    = flag.String("i", "", "Input RTSP URL")
	outputURL   = flag.String("o", "", "Output URL (HTTP, UDP or RTP)")
	mode        = flag.String("m", "r", "Mode: one of f,h,u,r or d")
	flags       = flag.Int("f", 0, "Flags: see readme for explanation")
	frameRate   = flag.Int("r", defaultFrameRate, "Input video frame rate (25fps by default)")
	selectedPID = flag.Int("p", defaultPID, "Select packets with this packet ID (PID)")
)

func main() {
	setUpDirs()
	flag.Parse()

	if *inputURL == "" {
		log.Fatal("Input (-i) required\n")
	}

	switch *mode {
	case "f":
		sendClip = sendClipToFile
	case "h":
		sendClip = sendClipToHTTP
		if *outputURL == "" {
			*outputURL = defaultHTTPOutput
		}
	case "u":
		sendClip = sendClipToUDP
		packetsPerFrame = udpPackets
		if *outputURL == "" {
			*outputURL = defaultUDPOutput
		}
	case "r":
		sendClip = sendClipToRTP
		packetsPerFrame = rtpPackets
		if *outputURL == "" {
			*outputURL = defaultRTPOutput
		}
	case "d":
		//sendClip = sendClipToStdout
	default:
		log.Fatalf("Invalid mode %s\n", *mode)
	}

	if *flags&filterFixContinuity != 0 && *flags&dumpProgramInfo != 0 {
		log.Fatal("Cannot combine filterFixContinuity and dumpProgramInfo flags\n")
	}

	ringBuffer = ringbuffer.NewRingBuffer(bufferSize, mp2tPacketSize*mp2tMaxPackets)
	inputErrChan = make(chan error, 10)
	outputErrChan = make(chan error, 10)

	go input(*inputURL, *outputURL)
	go output(*outputURL)

	for {
		select {
		default:
		case err := <-inputErrChan:
			fmt.Fprintln(os.Stderr, err)
			fmt.Fprintln(os.Stderr, "Trying again in 10s")
			time.Sleep(10 * time.Second)
			go input(*inputURL, *outputURL)
		case err := <-outputErrChan:
			fmt.Fprintln(os.Stderr, err)
			fmt.Fprintln(os.Stderr, "Attempting to write again!")
		}
	}
}

// setUpDirs sets directories based on the OS that Revid is running on
func setUpDirs() {
	switch runtime.GOOS {
	case "windows":
		ffmpegPath = "C:/ffmpeg/ffmpeg"
		tempDir = "tmp/"
	case "darwin":
		ffmpegPath = "/usr/local/bin/ffmpeg"
		tempDir = "/tmp/"
	default:
		ffmpegPath = "/home/$USER/bin/ffmpeg"
		tempDir = "/tmp/"
	}
}

// input handles the reading from the specified input
func input(input string, output string) {
	fmt.Printf("Reading video from %s\n", input)
	// (re)initialize globals
	clipCount = 0
	expectCC = -1
	dumpCC = -1
	dumpPCRBase = 0
	rtpSequenceNum = uint16(rand.Intn(1 << 15))

	// for UDP and RTP only dial once
	var err error
	if strings.HasPrefix(output, "udp://") || strings.HasPrefix(output, "rtp://") {
		conn, err = net.Dial("udp", output[6:])
		if err != nil {
			inputErrChan <- err
			return
		}
	}

	sess := rtsp.NewSession()
	res, err := sess.Options(rtspUrl)
	if err != nil {
		log.Fatalln(err)
	}
	fmt.Println("Options:")
	fmt.Println(res)

	res, err = sess.Describe(rtspUrl)
	if err != nil {
		log.Fatalln(err)
	}
	fmt.Println("Describe:")
	fmt.Println(res)

	p, err := rtsp.ParseSdp(&io.LimitedReader{R: res.Body, N: res.ContentLength})
	if err != nil {
		log.Fatalln(err)
	}
	log.Printf("%+v", p)

	fmt.Println("Setting up!")
	rtpPort, rtcpPort := 17300, 17319
	res, err = sess.Setup(rtpUrl, fmt.Sprintf("RTP/AVP;unicast;client_port=%d-%d", rtpPort, rtcpPort))
	if err != nil {
		log.Fatalln(err)
	}
	log.Println(res)

	fmt.Println("Playing !")
	res, err = sess.Play(rtspUrl, res.Header.Get("Session"))
	if err != nil {
		log.Fatalln(err)
	}
	log.Println(res)

	// create udp connection for rtp stuff
	rtpLaddr, err := net.ResolveUDPAddr("udp", "192.168.0.109:17300")
	if err != nil {
		fmt.Println("Local rtp addr not set!")
	}
	rtpAddr, err := net.ResolveUDPAddr("udp", "192.168.0.50:17300")
	if err != nil {
		fmt.Println("Resolving rtp address didn't work!")
	}
	rtpConn, err := net.DialUDP("udp", rtpLaddr, rtpAddr)
	if err != nil {
		fmt.Println("Rtp dial didn't work!")
	}

	// Create udp connection for rtcp stuff
	rtcpLaddr, err := net.ResolveUDPAddr("udp", "192.168.0.109:17319")
	if err != nil {
		fmt.Println("Local ")
	}
	rtcpAddr, err := net.ResolveUDPAddr("udp", "192.168.0.50:17301")
	if err != nil {
		fmt.Println("resolving rtcp address didn't work!")
	}
	rtcpConn, err := net.DialUDP("udp", rtcpLaddr, rtcpAddr)
	if err != nil {
		fmt.Println("Rtcp dial didnt't work!")
	}
	rtpSession := packets.NewSession(rtpConn,rtcpConn)
	converter := packets.NewRtpToTsConverter()
	go func(){
		for{
			select {
			default:
			case aPacket := <-rtpSession.RtpChan:
				converter.InputChan<-aPacket
			}
		}
	}()
	go converter.Convert()
	clipSize := 0
	packetCount := 0
	now := time.Now()
	prevTime := now
	fmt.Printf("Looping\n")


	startPackets := [][]byte{
		{71,64,17,16,0,66,240,65,0,1,193,0,0,255,1,255,0,1,252,128,48,72,46,1,6,70,70,109,112,101,103,37,115,116,114,101,97,109,101,100,32,98,121,32,116,104,101,32,71,101,111,86,105,115,105,111,110,32,82,116,115,112,32,83,101,114,118,101,114,99,176,214,195,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255},
		{71,64,0,16,0,0,176,13,0,1,193,0,0,0,1,240,0,42,177,4,178,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255},
		/*PMT*/{71,80,0,16,
		/*Start of payload*/
		0,2,176,18,0,1,193,0,0,255,255,240,0,27,225,0,240,0,193,91,65,224,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255},
	}

	donePSI := false

	for {
		if clip, err := ringBuffer.Get(); err != nil {
			inputErrChan <- err
			return
		} else {
			ii := 0
			for {
				upperBound := clipSize + mp2tPacketSize

				if ii < 3 && !donePSI {
					packetByteSlice := startPackets[ii]
					copy(clip[clipSize:upperBound],packetByteSlice)
					ii++
				} else {
					donePSI = true
					packet := <-converter.TsChan
					packetByteSlice := packet.ToByteSlice()
					copy(clip[clipSize:upperBound],packetByteSlice)
				}
				//fmt.Println(clip[clipSize:upperBound])
				packetCount++
				clipSize += mp2tPacketSize
				// send if (1) our buffer is full or (2) 1 second has elapsed and we have % packetsPerFrame
				now = time.Now()
				if (packetCount == mp2tMaxPackets) ||
					(now.Sub(prevTime) > clipDuration*time.Second && packetCount%packetsPerFrame == 0) {
					clipCount++
					if err := ringBuffer.DoneWriting(clipSize); err != nil {
						inputErrChan <- err
						return
					}
					clipSize = 0
					packetCount = 0
					prevTime = now
					break
				}
			}
		}
	}
}

// output handles the writing to specified output
func output(output string) {
	elapsedTime := time.Duration(0)
	now := time.Now()
	prevTime := now
	for {
		if clip, err := ringBuffer.Read(); err == nil {
			now := time.Now()
			for err = sendClip(clip, output, conn); err != nil; {
				outputErrChan <- err
				err = sendClip(clip, output, conn)
			}
			deltaTime := now.Sub(prevTime)
			elapsedTime += deltaTime
			if elapsedTime > bitrateOutputDelay*time.Second {
				noOfBits := float64(len(clip)*8) / 1024.0 // convert bytes to kilobits
				fmt.Printf("Bitrate: %d kbps\n", int64(noOfBits/float64(deltaTime/1e9)))
				elapsedTime = time.Duration(0)
			}
			prevTime = now
			if err := ringBuffer.DoneReading(); err != nil {
				outputErrChan <- err
			}
		}
	}
}

// sendClipToFile writes a video clip to a /tmp file.
func sendClipToFile(clip []byte, _ string, _ net.Conn) error {
	filename := fmt.Sprintf(tempDir+"vid%03d.ts", clipCount)
	fmt.Printf("Writing %s (%d bytes)\n", filename, len(clip))
	err := ioutil.WriteFile(filename, clip, 0644)
	if err != nil {
		return fmt.Errorf("Error writing file %s: %s", filename, err)
	}
	return nil
}

// sendClipToHTPP posts a video clip via HTTP, using a new TCP connection each time.
func sendClipToHTTP(clip []byte, output string, _ net.Conn) error {
	timeout := time.Duration(httpTimeOut * time.Second)
	client := http.Client{
		Timeout: timeout,
	}
	hash := md5.Sum(clip)
	url := output + strconv.Itoa(len(clip)) + "." + hex.EncodeToString(hash[:]) // NB: append size.digest to output
	fmt.Printf("Posting %s (%d bytes)\n", url, len(clip))
	resp, err := client.Post(url, "video/mp2t", bytes.NewReader(clip)) // lighter than NewBuffer
	if err != nil {
		return fmt.Errorf("Error posting to %s: %s", output, err)
	}
	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)
	if err == nil {
		fmt.Printf("%s\n", body)
	}
	return err
}

// sendClipToUDP sends a video clip over UDP.
func sendClipToUDP(clip []byte, _ string, conn net.Conn) error {
	size := udpPackets * mp2tPacketSize
	fmt.Printf("Sending %d UDP packets of size %d (%d bytes)\n", len(clip)/size, size, len(clip))
	for offset := 0; offset < len(clip); offset += size {
		pkt := clip[offset : offset+size]
		_, err := conn.Write(pkt)
		if err != nil {
			return fmt.Errorf("UDP write error %s. Is your player listening?", err)
		}
	}
	return nil
}

// sendClipToRTP sends a video clip over RTP.
func sendClipToRTP(clip []byte, _ string, conn net.Conn) error {
	size := rtpPackets * mp2tPacketSize
	fmt.Printf("Sending %d RTP packets of size %d (%d bytes)\n",
		len(clip)/size, size+rtpHeaderSize, len(clip))
	pkt := make([]byte, rtpHeaderSize+rtpPackets*mp2tPacketSize)
	for offset := 0; offset < len(clip); offset += size {
		rtpEncapsulate(clip[offset:offset+size], pkt)
		_, err := conn.Write(pkt)
		if err != nil {
			return fmt.Errorf("RTP write error %s. Is your player listening?", err)
		}
	}
	return nil
}

// checkContinuityCounts checks that the continuity of the clip is correct
func checkContinuityCounts(clip []byte) error {
	for offset := 0; offset < len(clip); offset += mp2tPacketSize {
		dumpCC = -1
		pkt := clip[offset : offset+mp2tPacketSize]
		cc := int(pkt[3] & 0xf)
		if dumpCC != -1 && cc != dumpCC {
			return fmt.Errorf("Continuity count out of order. Expected %v, Got: %v.", dumpCC, cc)
		}
		dumpCC = (cc + 1) % 16
	}
	return nil
}

// sendClipToStdout dumps video stats to stdout.
func sendClipToStdout(clip []byte) error {
	fmt.Printf("Dumping clip (%d bytes)\n", len(clip))
	/*
	if *flags&dumpProgramInfo != 0 {
		return mp2tDumpProgram(clip)
	}
	*/

	packetCount := 0
	discontinuities := 0
	var cc int

	for offset := 0; offset < len(clip); offset += mp2tPacketSize {
		packetCount++
		pkt := clip[offset : offset+mp2tPacketSize]

		pktPID, err := packet.Pid(pkt)
		if err != nil {
			return err
		}
		if pktPID != uint16(*selectedPID) {
			continue
		}

		if *flags&(dumpPacketHeader|dumpPacketPayload) != 0 {
			fmt.Printf("Packet #%d.%d\n", clipCount, packetCount)
		}

		hasPayload := pkt[3]&0x10 != 0
		if !hasPayload {
			continue // nothing to do
		}

		// extract interesting info from header
		tei := pkt[1] & 0x80 >> 7
		pusi := pkt[1] & 0x40 >> 6
		tp := pkt[1] & 0x20 >> 5
		tcs := pkt[3] & 0xc0 >> 6
		afc := pkt[3] & 0x30 >> 4
		cc = int(pkt[3] & 0xf)
		di := pkt[5] & 0x80

		if dumpCC != -1 && cc != dumpCC {
			discontinuities++
			fmt.Printf("Warning: Packet #%d.%d continuity counter out of order! Got %d, expected %d.\n",
				clipCount, packetCount, cc, dumpCC)
		}
		dumpCC = (cc + 1) % 16

		//if *flags&dumpPacketHeader != 0 {
			fmt.Printf("\t\tTEI=%d, PUSI=%d, TP=%d, TSC=%d, AFC=%d, CC=%d\n", tei, pusi, tp, tcs, afc, cc)
		//}

		if afc == 3 {
			// adaptation field, followed by payload
			afl := adaptationfield.Length(pkt)
			if adaptationfield.HasPCR(pkt) {
				pcrBase, pcrExt, _ := mp2tGetPCR(pkt)
				if *flags&dumpPacketHeader != 0 {
					fmt.Printf("\t\tAFL=%d, PCRbase=%d, PCRext=%d, DI=%v\n", afl, pcrBase, pcrExt, di)
				}
				if pcrBase < dumpPCRBase {
					fmt.Printf("Warning: PCRbase went backwards!\n")
				}
				dumpPCRBase = pcrBase
			} else if *flags&dumpPacketHeader != 0 {
				fmt.Printf("\t\tAFL=%d, DI=%v\n", afl, di)
			}
		}
		if *flags&dumpPacketPayload != 0 {
			fmt.Printf("\t\tPayload=%x\n", pkt)
		}

	}
	if *flags&dumpPacketStats != 0 {
		fmt.Printf("%d packets of size %d bytes (%d bytes, %d discontinuites)\n",
			packetCount, packet.PacketSize, packetCount*packet.PacketSize, discontinuities)
	}
	return nil
}

// mp2tDumpProgram dumps MPEG-TS Program Association Table (PAT) and Program Map Tables (PMT).
func mp2tDumpProgram(clip []byte) error {
	// NB: Comcast API requires a buffered reader
	reader := bufio.NewReader(bytes.NewReader(clip))

	_, err := packet.Sync(reader)
	if err != nil {
		return fmt.Errorf("Error reading sync byte: %s", err)
	}
	pat, err := psi.ReadPAT(reader)
	if err != nil {
		return fmt.Errorf("Error reading PAT: %s", err)
	}
	mp2tDumpPat(pat)

	var pmts []psi.PMT
	pm := pat.ProgramMap()
	for pn, pid := range pm {
		pmt, err := psi.ReadPMT(reader, pid)
		if err != nil {
			return fmt.Errorf("Error reading PMT: %s", err)
		}
		pmts = append(pmts, pmt)
		mp2tDumpPmt(pn, pmt)
	}
	return nil
}

func mp2tDumpPat(pat psi.PAT) {
	fmt.Printf("Pat\n")
	fmt.Printf("\tPMT PIDs %v\n", pat.ProgramMap())
	fmt.Printf("\tNumber of Programs %v\n", pat.NumPrograms())
}

func mp2tDumpPmt(pn uint16, pmt psi.PMT) {
	// pn = program number
	fmt.Printf("Program #%v PMT\n", pn)
	fmt.Printf("\tPIDs %v\n", pmt.Pids())
	fmt.Printf("\tElementary Streams")
	for _, es := range pmt.ElementaryStreams() {
		fmt.Printf("\t\tPID %v : StreamType %v\n", es.ElementaryPid(), es.StreamType())
		for _, d := range es.Descriptors() {
			fmt.Printf("\t\t\t%+v\n", d)
		}
	}
}

// Mp2tFixContinuity fixes discontinous MPEG-TS continuity counts (CC)
func mp2tFixContinuity(pkt []byte, pid uint16) bool {

	hasPayload, err := packet.ContainsPayload(pkt)
	if err != nil {
		fmt.Printf("Warning: Packet bad.\n")
		return false
	}
	if !hasPayload {
		return false
	}
	if pktPID, _ := packet.Pid(pkt); pktPID != pid {
		return false
	}
	fixed := false
	// extract continuity counter from 2nd nibble of 4th byte of header
	cc := int(pkt[3] & 0xf)
	if expectCC == -1 {
		expectCC = cc
	} else if cc != expectCC {
		fmt.Println("Have to fix")
		pkt[3] = pkt[3]&0xf0 | byte(expectCC&0xf)
		fixed = true
	}
	expectCC = (expectCC + 1) % 16
	return fixed
}

// Mp2tGetPCR extracts the Program Clock Reference (PCR) from an MPEG-TS packet (if any)
func mp2tGetPCR(pkt []byte) (uint64, uint32, bool) {
	if !adaptationfield.HasPCR(pkt) {
		return 0, 0, false
	}
	pcrBytes, _ := adaptationfield.PCR(pkt) // 6 bytes
	// first 33 bits are PCR base, next 6 bits are reserved, final 9 bits are PCR extension.
	pcrBase := uint64(binary.BigEndian.Uint32(pcrBytes[:4]))<<1 | uint64(pcrBytes[4]&0x80>>7)
	pcrExt := uint32(pcrBytes[4]&0x01)<<1 | uint32(pcrBytes[5])
	return pcrBase, pcrExt, true
}

// rtpEncapsulate encapsulates MPEG-TS packets within an RTP header,
// setting the payload type accordingly (to 33) and incrementing the RTP sequence number.
func rtpEncapsulate(mp2tPacket []byte, pkt []byte) {
	// RTP packet encapsulates the MP2T
	// first 12 bytes is the header
	// byte 0: version=2, padding=0, extension=0, cc=0
	pkt[0] = 0x80 // version (2)
	// byte 1: marker=0, pt = 33 (MP2T)
	pkt[1] = 33
	// bytes 2 & 3: sequence number
	binary.BigEndian.PutUint16(pkt[2:4], rtpSequenceNum)
	if rtpSequenceNum == ^uint16(0) {
		rtpSequenceNum = 0
	} else {
		rtpSequenceNum++
	}
	// bytes 4,5,6&7: timestamp
	timestamp := uint32(time.Now().UnixNano() / 1e6) // ms timestamp
	binary.BigEndian.PutUint32(pkt[4:8], timestamp)
	// bytes 8,9,10&11: SSRC
	binary.BigEndian.PutUint32(pkt[8:12], rtpSSRC)

	// payload follows
	copy(pkt[rtpHeaderSize:rtpHeaderSize+rtpPackets*mp2tPacketSize], mp2tPacket)
}