av/container/mts/encoder.go

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/*
NAME
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encoder.go
AUTHOR
Dan Kortschak <dan@ausocean.org>
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Saxon Nelson-Milton <saxon@ausocean.org>
LICENSE
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encoder.go is Copyright (C) 2017-2018 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 mts
import (
"fmt"
"io"
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"time"
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"bitbucket.org/ausocean/av/container/mts/meta"
"bitbucket.org/ausocean/av/container/mts/pes"
"bitbucket.org/ausocean/av/container/mts/psi"
)
// Some common manifestations of PSI
var (
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// standardPat is a minimal PAT.
standardPat = psi.PSI{
Pf: 0x00,
Tid: 0x00,
Ssi: true,
Pb: false,
Sl: 0x0d,
Tss: &psi.TSS{
Tide: 0x01,
V: 0,
Cni: true,
Sn: 0,
Lsn: 0,
Sd: &psi.PAT{
Pn: 0x01,
Pmpid: 0x1000,
},
},
}
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// standardPmt is a minimal PMT, without descriptors for time and location.
standardPmt = psi.PSI{
Pf: 0x00,
Tid: 0x02,
Ssi: true,
Sl: 0x12,
Tss: &psi.TSS{
Tide: 0x01,
V: 0,
Cni: true,
Sn: 0,
Lsn: 0,
Sd: &psi.PMT{
Pcrpid: 0x0100,
Pil: 0,
Essd: &psi.ESSD{
St: 0x1b,
Epid: 0x0100,
Esil: 0x00,
},
},
},
}
)
const (
psiInterval = 1 * time.Second
psiSendCount = 7
)
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// Meta allows addition of metadata to encoded mts from outside of this pkg.
// See meta pkg for usage.
//
// TODO: make this not global.
var Meta *meta.Data
var (
patTable = standardPat.Bytes()
pmtTable = standardPmt.Bytes()
)
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const (
sdtPid = 17
patPid = 0
pmtPid = 4096
videoPid = 256
// AudioPid is the Id for packets containing audio data
AudioPid = 210
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videoStreamID = 0xe0 // First video stream ID.
audioStreamID = 0xc0 // First audio stream ID.
)
// Video and Audio constants are used to communicate which media type will be encoded when creating a
// new encoder with NewEncoder.
const (
Video = iota
Audio
)
// Time related constants.
const (
// 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
// pcrFreq is the base Program Clock Reference frequency.
pcrFreq = 90000 // Hz
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)
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// Encoder encapsulates properties of an mpegts generator.
type Encoder struct {
dst io.Writer
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clock time.Duration
lastTime time.Time
writePeriod time.Duration
ptsOffset time.Duration
tsSpace [PacketSize]byte
pesSpace [pes.MaxPesSize]byte
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continuity map[int]byte
timeBasedPsi bool
pktCount int
psiSendCount int
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mediaPid int
streamID byte
psiLastTime time.Time
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}
// NewEncoder returns an Encoder with the specified media type and rate eg. if a video stream
// calls write for every frame, the rate will be the frame rate of the video.
func NewEncoder(dst io.Writer, rate float64, mediaType int) *Encoder {
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var mPid int
var sid byte
switch mediaType {
case Audio:
mPid = AudioPid
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sid = audioStreamID
case Video:
mPid = videoPid
sid = videoStreamID
}
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return &Encoder{
dst: dst,
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writePeriod: time.Duration(float64(time.Second) / rate),
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ptsOffset: ptsOffset,
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timeBasedPsi: true,
pktCount: 8,
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mediaPid: mPid,
streamID: sid,
continuity: map[int]byte{
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patPid: 0,
pmtPid: 0,
mPid: 0,
},
}
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}
const (
hasPayload = 0x1
hasAdaptationField = 0x2
)
const (
hasDTS = 0x1
hasPTS = 0x2
)
// TimeBasedPsi allows for the setting of the PSI writing method, therefore, if
// PSI is written based on some time duration, or based on a packet count.
// If b is true, then time based PSI is used, otherwise the PSI is written
// every sendCount.
func (e *Encoder) TimeBasedPsi(b bool, sendCount int) {
e.timeBasedPsi = b
e.psiSendCount = sendCount
e.pktCount = e.psiSendCount
}
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// Write implements io.Writer. Write takes raw video or audio data and encodes into mpegts,
// then sending it to the encoder's io.Writer destination.
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func (e *Encoder) Write(data []byte) (int, error) {
if len(data) > pes.MaxPesSize {
return 0, fmt.Errorf("data size too large (Max is %v): %v", pes.MaxPesSize, len(data))
}
now := time.Now()
if (e.timeBasedPsi && (now.Sub(e.psiLastTime) > psiInterval)) || (!e.timeBasedPsi && (e.pktCount >= e.psiSendCount)) {
e.pktCount = 0
err := e.writePSI()
if err != nil {
return 0, err
}
e.psiLastTime = now
}
// Prepare PES data.
pesPkt := pes.Packet{
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StreamID: e.streamID,
PDI: hasPTS,
PTS: e.pts(),
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Data: data,
HeaderLength: 5,
}
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buf := pesPkt.Bytes(e.pesSpace[:pes.MaxPesSize])
pusi := true
for len(buf) != 0 {
pkt := Packet{
PUSI: pusi,
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PID: uint16(e.mediaPid),
RAI: pusi,
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CC: e.ccFor(e.mediaPid),
AFC: hasAdaptationField | hasPayload,
PCRF: pusi,
}
n := pkt.FillPayload(buf)
buf = buf[n:]
if pusi {
// If the packet has a Payload Unit Start Indicator
// flag set then we need to write a PCR.
pkt.PCR = e.pcr()
pusi = false
}
_, err := e.dst.Write(pkt.Bytes(e.tsSpace[:PacketSize]))
if err != nil {
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return len(data), err
}
e.pktCount++
}
e.tick()
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return len(data), nil
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}
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// writePSI creates mpegts with pat and pmt tables - with pmt table having updated
// location and time data.
func (e *Encoder) writePSI() error {
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// Write PAT.
patPkt := Packet{
PUSI: true,
PID: PatPid,
CC: e.ccFor(PatPid),
AFC: HasPayload,
Payload: psi.AddPadding(patTable),
}
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_, err := e.dst.Write(patPkt.Bytes(e.tsSpace[:PacketSize]))
if err != nil {
return err
}
e.pktCount++
pmtTable, err = updateMeta(pmtTable)
if err != nil {
return err
}
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// Create mts packet from pmt table.
pmtPkt := Packet{
PUSI: true,
PID: PmtPid,
CC: e.ccFor(PmtPid),
AFC: HasPayload,
Payload: psi.AddPadding(pmtTable),
}
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_, err = e.dst.Write(pmtPkt.Bytes(e.tsSpace[:PacketSize]))
if err != nil {
return err
}
e.pktCount++
return nil
}
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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.writePeriod
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}
// pts retuns the current presentation timestamp.
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func (e *Encoder) pts() uint64 {
return uint64((e.clock + e.ptsOffset).Seconds() * pcrFreq)
}
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// pcr returns the current program clock reference.
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func (e *Encoder) pcr() uint64 {
return uint64(e.clock.Seconds() * pcrFreq)
}
// ccFor returns the next continuity counter for pid.
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func (e *Encoder) ccFor(pid int) byte {
cc := e.continuity[pid]
const continuityCounterMask = 0xf
e.continuity[pid] = (cc + 1) & continuityCounterMask
return cc
}
// updateMeta adds/updates a metaData descriptor in the given psi bytes using data
// contained in the global Meta struct.
func updateMeta(b []byte) ([]byte, error) {
p := psi.PSIBytes(b)
err := p.AddDescriptor(psi.MetadataTag, Meta.Encode())
return []byte(p), err
}