mirror of https://bitbucket.org/ausocean/av.git
281 lines
5.7 KiB
Go
281 lines
5.7 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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"io"
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"time"
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"bitbucket.org/ausocean/av/stream/mts/meta"
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"bitbucket.org/ausocean/av/stream/mts/pes"
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"bitbucket.org/ausocean/av/stream/mts/psi"
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)
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// Some common manifestations of PSI
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var (
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// standardPat is a minimal PAT.
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standardPat = psi.PSI{
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Pf: 0x00,
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Tid: 0x00,
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Ssi: true,
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Pb: false,
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Sl: 0x0d,
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Tss: &psi.TSS{
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Tide: 0x01,
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V: 0,
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Cni: true,
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Sn: 0,
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Lsn: 0,
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Sd: &psi.PAT{
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Pn: 0x01,
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Pmpid: 0x1000,
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},
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},
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}
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// standardPmt is a minimal PMT, without descriptors for time and location.
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standardPmt = psi.PSI{
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Pf: 0x00,
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Tid: 0x02,
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Ssi: true,
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Sl: 0x12,
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Tss: &psi.TSS{
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Tide: 0x01,
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V: 0,
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Cni: true,
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Sn: 0,
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Lsn: 0,
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Sd: &psi.PMT{
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Pcrpid: 0x0100,
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Pil: 0,
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Essd: &psi.ESSD{
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St: 0x1b,
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Epid: 0x0100,
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Esil: 0x00,
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},
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},
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},
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}
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)
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const (
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psiInterval = 1 * time.Second
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)
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// Meta allows addition of metadata to encoded mts from outside of this pkg.
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// See meta pkg for usage.
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//
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// TODO: make this not global.
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var Meta *meta.Data
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var (
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patTable = standardPat.Bytes()
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pmtTable = standardPmt.Bytes()
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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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lastTime time.Time
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frameInterval time.Duration
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ptsOffset time.Duration
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tsSpace [PacketSize]byte
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pesSpace [pes.MaxPesSize]byte
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continuity map[int]byte
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psiLastTime time.Time
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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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now := time.Now()
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if now.Sub(e.psiLastTime) > psiInterval {
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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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e.psiLastTime = now
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}
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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(e.pesSpace[:pes.MaxPesSize])
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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(e.tsSpace[:PacketSize]))
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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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// writePSI creates mpegts with pat and pmt tables - with pmt table having updated
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// location and time data.
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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: psi.AddPadding(patTable),
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}
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_, err := e.dst.Write(patPkt.Bytes(e.tsSpace[:PacketSize]))
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if err != nil {
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return err
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}
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pmtTable, err = updateMeta(pmtTable)
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if err != nil {
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return err
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}
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// Create mts packet from pmt table.
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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: psi.AddPadding(pmtTable),
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}
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_, err = e.dst.Write(pmtPkt.Bytes(e.tsSpace[:PacketSize]))
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if err != nil {
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return err
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}
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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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now := time.Now()
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e.clock += now.Sub(e.lastTime)
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e.lastTime = now
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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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// updateMeta adds/updates a metaData descriptor in the given psi bytes using data
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// contained in the global Meta struct.
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func updateMeta(b []byte) ([]byte, error) {
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p := psi.PSIBytes(b)
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err := p.AddDescriptor(psi.MetadataTag, Meta.Encode())
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return []byte(p), err
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}
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