av/generator/mpegts_generator.go

/*
NAME
  mpegts_generator.go

DESCRIPTION
  See Readme.md

AUTHOR
  Saxon Nelson-Milton <saxon@ausocean.org>

LICENSE
  mpegts_generator.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 http://www.gnu.org/licenses.
*/
package generator

import (
	"bitbucket.org/ausocean/av/mpegts"
	"bitbucket.org/ausocean/av/pes"
)

const mpegtsPacketSize = 184

// TODO: really need to finish the at and pmt stuff - this is too hacky
var (
	patTableStart = []byte{0, 0, 176, 13, 0, 1, 193, 0, 0, 0, 1, 240, 0, 42, 177, 4, 178}
	patTable      []byte
	pmtTableStart = []byte{0, 2, 176, 18, 0, 1, 193, 0, 0, 0xE1, 0x00, 0xF0, 0, 0x1B, 0xE1, 0, 0xF0, 0, 0x15, 0xBD, 0x4D, 0x56}
	pmtTable      []byte
)

// genPatAndPmt generates the rest of the pat and pmt tables i.e. fills them
// with 0xFFs - because it looks ugly to hardcode above. This is called through
// NewMpegtsgenerator
func genPatAndPmt() {
	patTable = make([]byte, 0, mpegtsPacketSize)
	patTable = append(patTable, patTableStart...)
	for i := len(pmtTableStart); i < mpegtsPacketSize-len(pmtTableStart); i++ {
		pmtTable[i] = 255
	}
	pmtTable = make([]byte, 0, mpegtsPacketSize)
	pmtTable = append(pmtTable, pmtTableStart...)
	for i := len(patTableStart); i < mpegtsPacketSize-len(patTableStart); i++ {
		pmtTable[i] = 255
	}
}

const (
	SdtPid              = 17
	PatPid              = 0
	pmtPid              = 4096
	videoPid            = 256
	streamID            = 0xE0
	outputChanSize      = 100
	inputChanSize       = 10000
	pesPktChanSize      = 1000
	payloadByteChanSize = 100000
	ptsOffset           = .7
	maxCC               = 15
)

// tsGenerator encapsulates properties of an mpegts generator.
type tsGenerator struct {
	outputChan      chan []byte
	nalInputChan    chan []byte
	currentTsPacket *mpegts.MpegTsPacket
	payloadByteChan chan byte
	currentCC       byte
	currentPtsTime  float64
	currentPcrTime  float64
	fps             uint
	pesPktChan      chan []byte
	ccMap           map[int]int
	isGenerating    bool
}

// getInputChan returns a handle to the nalInputChan (inputChan) so that nal units
// can be passed to the generator and processed
func (g *tsGenerator) GetInputChan() chan []byte {
	return g.nalInputChan
}

// GetOutputChan returns a handle to the generator output chan where the mpegts
// packets will show up once ready to go
func (g *tsGenerator) GetOutputChan() chan []byte {
	return g.outputChan
}

// NewTsGenerator returns an instance of the tsGenerator struct
func NewTsGenerator(fps uint) (g *tsGenerator) {
	g = new(tsGenerator)
	g.outputChan = make(chan []byte, outputChanSize)
	g.nalInputChan = make(chan []byte, inputChanSize)
	g.currentCC = 0
	g.fps = fps
	g.currentPcrTime = 0.0
	g.currentPtsTime = ptsOffset
	g.pesPktChan = make(chan []byte, pesPktChanSize)
	g.payloadByteChan = make(chan byte, payloadByteChanSize)
	g.ccMap = make(map[int]int, 4)
	g.ccMap[SdtPid] = 0
	g.ccMap[PatPid] = 0
	g.ccMap[pmtPid] = 0
	g.ccMap[videoPid] = 0
	genPatAndPmt()
	g.isGenerating = false
	return
}

// getPts retuns the next presentation timestamp for the tsGenerator t.
func (g *tsGenerator) genPts() (pts uint64) {
	pts = uint64(g.currentPtsTime * float64(90000))
	g.currentPtsTime += 1.0 / float64(g.fps)
	return
}

// genPcr returns the next program clock reference for the tsGenerator g
func (g *tsGenerator) genPcr() (pcr uint64) {
	pcr = uint64(g.currentPcrTime * float64(90000))
	g.currentPcrTime += 1.0 / float64(g.fps)
	return
}

// Start is called when we would like generation to begin, i.e. we would like
// the generator to start taking input data and creating mpegts packets
func (g *tsGenerator) Start() {
	g.isGenerating = true
	go g.generate()
}

func (g *tsGenerator) Stop() {
	g.isGenerating = false
}

// getCC returns the next continuity counter for a particular pid
func (g *tsGenerator) getCC(pid int) int {
	temp := g.ccMap[pid]
	if g.ccMap[pid]++; g.ccMap[pid] > maxCC {
		g.ccMap[pid] = 0
	}
	return temp
}

// generate handles the incoming data and generates equivalent mpegts packets -
// sending them to the output channel
func (g *tsGenerator) generate() {
	for {
		select {
		case nalUnit := <-g.nalInputChan:
			pesPkt := pes.PESPacket{
				StreamID:     streamID,
				PDI:          byte(2),
				PTS:          g.genPts(),
				Data:         nalUnit,
				HeaderLength: 5,
			}
			g.pesPktChan <- pesPkt.ToByteSlice()
		case pesPkt := <-g.pesPktChan:
			for ii := range pesPkt {
				g.payloadByteChan <- pesPkt[ii]
			}
			pusi := true
			for len(g.payloadByteChan) > 0 {
				pkt := mpegts.MpegTsPacket{
					PUSI: pusi,
					PID:  videoPid,
					RAI:  pusi,
					CC:   byte(g.getCC(videoPid)),
					AFC:  byte(3),
					PCRF: pusi,
				}
				pkt.FillPayload(g.payloadByteChan)

				// TODO: create consts for AFC parameters
				if pusi {
					// Create pat table
					patPkt := mpegts.MpegTsPacket{
						PUSI:    pusi,
						PID:     PatPid,
						CC:      byte(g.getCC(PatPid)),
						AFC:     1,
						Payload: patTable,
					}
					g.outputChan <- patPkt.ToByteSlice()
					// Create pmt table
					pmtPkt := mpegts.MpegTsPacket{
						PUSI:    pusi,
						PID:     pmtPid,
						CC:      byte(g.getCC(pmtPid)),
						AFC:     1,
						Payload: pmtTable,
					}
					g.outputChan <- pmtPkt.ToByteSlice()
					// If pusi then we need to gen a pcr
					pkt.PCR = g.genPcr()
					pusi = false
				}
				g.outputChan <- pkt.ToByteSlice()
			}
		}
	}
}