av/packets/RtpToTsConverter.go

/*
NAME
  RtpToTsConverter.go - provides utilities for the conversion of Rtp packets
  to equivalent MpegTs packets.

DESCRIPTION
  See Readme.md

AUTHOR
  Saxon Nelson-Milton <saxon.milton@gmail.com>

LICENSE
  RtpToTsConverter.go is Copyright (C) 2017 the Australian Ocean Lab (AusOcean)

  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).
*/

package packets

import "fmt"

type RtpToTsConverter interface {
  Convert()
}

type rtpToTsConverter struct {
  TsChan <-chan *MpegTsPacket
  tsChan chan<- *MpegTsPacket
  currentTsPacket *MpegTsPacket
  payloadByteChan chan byte
  currentCC byte
}

func NewRtpToTsConverter() (c *rtpToTsConverter) {
  c = new(rtpToTsConverter)
  tsChan := make(chan *MpegTsPacket,100)
  c.TsChan = tsChan
  c.tsChan = tsChan
  c.payloadByteChan = make(chan byte, 10000)
  c.currentCC = 0
  return
}

func (c* rtpToTsConverter) Convert(rtpSession *Session) {
  nalUnitChan := make(chan *NALUnit, 1000)
  // Get nal units from incoming rtp
  go func(){
    for {
      rtpPacket := <-rtpSession.RtpChan
      if GetNalType( rtpPacket.Payload ) == 28 {
        nalUnitChan<-ParseNALUnit(rtpPacket.Payload)
      }
    }
  }()
  // Create PES packets from NAl units
  pesPktChan := make(chan []byte, 100)
  go func(){
    pesDataChan := make(chan []byte, 100)
    for {
      nalUnit:=<-nalUnitChan
      if nalUnit.Start {
        pesDataChanLen = len(pesDataChan)
        if pesDataChanLen > 0 {
          pesPkt := new(PESPacket)
          pesPkt.StreamID = 0xE0
          pesPkt.Length = 24 + pesDataChanLen
          pesPkt.ScramblingControl = 0
          pesPkt.Priority = true
          pesPkt.DAI = false
          pesPkt.Copyright = false
          pesPkt.Original = true
          pesPkt.PDI = false
          pesPkt.ESCR = false
          pesPkt.ESRate = false
          pesPkt.DSMTrickMode = false
          pesPkt.ACI = false
          pesPkt.CRC = false
          pesPkt.Ext = false
          pesPkt.HeaderLength = 0
          pesPkt.Data = make([]byte,pesDataChanLen)
          for ii:=0; ii<pesDataChanLen; ii++ {
            pesPkt.Data[i] = <-pesDataChan
          }
          pesPktChan<-pesPkt.ToByteSlice()
        }
        pesDataChan<-nalUnit.ToByteSlice()
      }
    }
  }()
  // Create mpegts using pes packets
  for {
    pesPkt := <-pesPktChan
    for ii:=range pesPkt {
      c.payloadByteChan<-pesPkt[ii]
    }
    firstPacket:=true
    for len(c.payloadByteChan) > 0 {
      lengthOfByteChan := len(c.payloadByteChan)
      c.currentTsPacket = new(MpegTsPacket)
      c.currentTsPacket.SyncByte = 0x47
      c.currentTsPacket.TEI = false
      c.currentTsPacket.PUSI = false
      if firstPacket  { // if it's the start of the payload
        c.currentTsPacket.PUSI = true
        firstPacket = false
      }
      c.currentTsPacket.Priority = false
      c.currentTsPacket.PID = 256
      c.currentTsPacket.TSC = 0
      c.currentTsPacket.CC = c.currentCC
      if c.currentCC++; c.currentCC > 15 { c.currentCC = 0 }
      payloadLength := 182
      if lengthOfByteChan < 182 {
        payloadLength = lengthOfByteChan
      }
      c.currentTsPacket.AFC = 3
      stuffingLength := 182-payloadLength
      c.currentTsPacket.AF = make([]byte,2 + stuffingLength) // adaptationfield flag length = 16
      c.currentTsPacket.AF[0] = byte(1 + stuffingLength)
      c.currentTsPacket.AF[1] = 0
      if c.currentTsPacket.PUSI {
        c.currentTsPacket.AF[1] = 0x40
      }
      for ii := 0; ii < stuffingLength; ii++ {
        c.currentTsPacket.AF[2+ii] = 0xFF
      }
      c.currentTsPacket.Payload = make([]byte, payloadLength)
      for ii:=0; ii < payloadLength; ii++ {
        c.currentTsPacket.Payload[ii] = <-c.payloadByteChan
      }
      c.tsChan<-c.currentTsPacket
    }
  }
}