mirror of https://bitbucket.org/ausocean/av.git
303 lines
6.5 KiB
Go
303 lines
6.5 KiB
Go
/*
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NAME
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encoder.go
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DESCRIPTION
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See Readme.md
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AUTHOR
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Dan Kortschak <dan@ausocean.org>
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Saxon Nelson-Milton <saxon@ausocean.org>
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LICENSE
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encoder.go is Copyright (C) 2017-2018 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package mts
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import (
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"encoding/binary"
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"hash/crc32"
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"io"
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"math/bits"
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"time"
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"bitbucket.org/ausocean/av/stream/mts/pes"
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)
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const (
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psiPacketSize = 184
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psiSendCount = 100
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)
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// TODO: Finish off mts/psi so that we can create pat and pmt tables instead
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// of hardcoding.
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var (
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patTable = []byte{
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0x00, // pointer
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// ---- section included in data sent to CRC32 during check
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// table header
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0x00, // table id
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0xb0, // section syntax indicator:1|private bit:1|reserved:2|section length:2|more bytes...:2
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0x0d, // more bytes...
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// syntax section
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0x00, 0x01, // table id extension
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0xc1, // reserved bits:3|version:5|use now:1
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0x00, // section number
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0x00, // last section number
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// table data
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0x00, 0x01, // Program number
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0xf0, 0x00, // reserved:3|program map PID:13
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// 0x2a, 0xb1, 0x04, 0xb2, // CRC
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// ----
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}
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pmtTable = []byte{
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0x00, // pointer
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// ---- section included in data sent to CRC32 during check
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// table header
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0x02, // table id
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0xb0, // section syntax indicator:1|private bit:1|reserved:2|section length:2|more bytes...:2
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0x12, // more bytes...
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// syntax section
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0x00, 0x01, // table id extension
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0xc1, // reserved bits:3|version:5|use now:1
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0x00, // section number
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0x00, // last section number
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// table data
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0xe1, 0x00, // reserved:3|PCR PID:13
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0xf0, 0x00, // reserved:4|unused:2|program info length:10
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// No program descriptors since program info length is 0.
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// elementary stream info data
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0x1b, // stream type
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0xe1, 0x00, // reserved:3|elementary PID:13
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0xf0, 0x00, // reserved:4|unused:2|ES info length:10
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// No elementary stream descriptors since ES info length is 0.
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// 0x15, 0xbd, 0x4d, 0x56, // CRC
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// ----
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}
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)
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func init() {
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// Generate IEEE polynomial table
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// for the big-endian algorithm.
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crcTable := crc32_MakeTable(bits.Reverse32(crc32.IEEE))
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patTable = completePSI(patTable, crcTable)
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pmtTable = completePSI(pmtTable, crcTable)
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}
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func completePSI(psi []byte, tab *crc32.Table) []byte {
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var buf [4]byte
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crc := crc32_Update(0xffffffff, tab, psi[1:])
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binary.BigEndian.PutUint32(buf[:], crc)
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dst := make([]byte, len(psi), psiPacketSize)
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copy(dst, psi)
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dst = append(dst, buf[:]...)
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for len(dst) < cap(dst) {
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dst = append(dst, 0xff)
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}
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return dst
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}
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func crc32_MakeTable(poly uint32) *crc32.Table {
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var t crc32.Table
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for i := range t {
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crc := uint32(i) << 24
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for j := 0; j < 8; j++ {
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if crc&0x80000000 != 0 {
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crc = (crc << 1) ^ poly
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} else {
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crc <<= 1
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}
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}
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t[i] = crc
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}
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return &t
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}
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func crc32_Update(crc uint32, tab *crc32.Table, p []byte) uint32 {
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for _, v := range p {
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crc = tab[byte(crc>>24)^v] ^ (crc << 8)
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}
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return crc
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}
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const (
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sdtPid = 17
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patPid = 0
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pmtPid = 4096
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videoPid = 256
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streamID = 0xe0 // First video stream ID.
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)
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// Time related constants.
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const (
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// ptsOffset is the offset added to the clock to determine
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// the current presentation timestamp,
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ptsOffset = 700 * time.Millisecond
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// pcrFreq is the base Program Clock Reference frequency.
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pcrFreq = 90000 // Hz
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)
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// Encoder encapsulates properties of an mpegts generator.
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type Encoder struct {
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dst io.Writer
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clock time.Duration
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frameInterval time.Duration
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ptsOffset time.Duration
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psiCount uint
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continuity map[int]byte
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}
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// NewEncoder returns an Encoder with the specified frame rate.
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func NewEncoder(dst io.Writer, fps float64) *Encoder {
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return &Encoder{
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dst: dst,
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frameInterval: time.Duration(float64(time.Second) / fps),
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ptsOffset: ptsOffset,
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continuity: map[int]byte{
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patPid: 0,
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pmtPid: 0,
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videoPid: 0,
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},
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}
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}
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const (
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hasPayload = 0x1
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hasAdaptationField = 0x2
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)
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const (
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hasDTS = 0x1
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hasPTS = 0x2
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)
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// generate handles the incoming data and generates equivalent mpegts packets -
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// sending them to the output channel
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func (e *Encoder) Encode(nalu []byte) error {
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if e.psiCount <= 0 {
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err := e.writePSI()
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if err != nil {
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return err
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}
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}
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e.psiCount -= 1
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// Prepare PES data.
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pesPkt := pes.Packet{
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StreamID: streamID,
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PDI: hasPTS,
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PTS: e.pts(),
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Data: nalu,
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HeaderLength: 5,
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}
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buf := pesPkt.Bytes()
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pusi := true
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for len(buf) != 0 {
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pkt := Packet{
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PUSI: pusi,
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PID: videoPid,
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RAI: pusi,
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CC: e.ccFor(videoPid),
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AFC: hasAdaptationField | hasPayload,
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PCRF: pusi,
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}
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n := pkt.FillPayload(buf)
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buf = buf[n:]
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if pusi {
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// If the packet has a Payload Unit Start Indicator
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// flag set then we need to write a PCR.
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pkt.PCR = e.pcr()
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pusi = false
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}
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_, err := e.dst.Write(pkt.Bytes())
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if err != nil {
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return err
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}
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}
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e.tick()
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return nil
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}
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func (e *Encoder) writePSI() error {
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// Write PAT
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patPkt := Packet{
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PUSI: true,
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PID: patPid,
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CC: e.ccFor(patPid),
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AFC: hasPayload,
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Payload: patTable,
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}
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_, err := e.dst.Write(patPkt.Bytes())
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if err != nil {
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return err
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}
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// Write PMT.
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pmtPkt := Packet{
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PUSI: true,
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PID: pmtPid,
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CC: e.ccFor(pmtPid),
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AFC: hasPayload,
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Payload: pmtTable,
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}
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_, err = e.dst.Write(pmtPkt.Bytes())
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if err != nil {
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return err
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}
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e.psiCount = psiSendCount
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return nil
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}
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// tick advances the clock one frame interval.
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func (e *Encoder) tick() {
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e.clock += e.frameInterval
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}
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// pts retuns the current presentation timestamp.
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func (e *Encoder) pts() uint64 {
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return uint64((e.clock + e.ptsOffset).Seconds() * pcrFreq)
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}
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// pcr returns the current program clock reference.
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func (e *Encoder) pcr() uint64 {
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return uint64(e.clock.Seconds() * pcrFreq)
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}
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// ccFor returns the next continuity counter for pid.
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func (e *Encoder) ccFor(pid int) byte {
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cc := e.continuity[pid]
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const continuityCounterMask = 0xf
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e.continuity[pid] = (cc + 1) & continuityCounterMask
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return cc
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}
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