mirror of https://bitbucket.org/ausocean/av.git
139 lines
3.4 KiB
Go
139 lines
3.4 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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Saxon Nelson-Milton (saxon@ausocean.org)
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LICENSE
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encoder.go is Copyright (C) 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 rtp
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import (
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"io"
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"math/rand"
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"time"
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)
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const (
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yes = 1
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no = 0
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defaultPktType = 33
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timestampFreq = 90000 // Hz
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mtsSize = 188
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bufferSize = 1000
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sendSize = 7 * 188
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)
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// Encoder implements io writer and provides functionality to wrap data into
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// rtp packets
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type Encoder struct {
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dst io.Writer
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ssrc uint32
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seqNo uint16
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clock time.Duration
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frameInterval time.Duration
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lastTime time.Time
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fps int
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buffer []byte
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pktSpace [defPktSize]byte
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}
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// NewEncoder returns a new Encoder type given an io.Writer - the destination
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// after encoding and the desired fps
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func NewEncoder(dst io.Writer, fps int) *Encoder {
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return &Encoder{
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dst: dst,
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ssrc: rand.Uint32(),
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frameInterval: time.Duration(float64(time.Second) / float64(fps)),
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fps: fps,
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buffer: make([]byte, 0),
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}
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}
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// Write provides an interface between a prior encoder and this rtp encoder,
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// so that multiple layers of packetization can occur.
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func (e *Encoder) Write(data []byte) (int, error) {
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e.buffer = append(e.buffer, data...)
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if len(e.buffer) < sendSize {
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return len(data), nil
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}
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buf := e.buffer
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for len(buf) != 0 {
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l := min(sendSize, len(buf))
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err := e.Encode(buf[:l])
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if err != nil {
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return len(data), err
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}
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buf = buf[l:]
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}
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e.buffer = e.buffer[:0]
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return len(data), nil
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}
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func min(a, b int) int {
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if a < b {
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return a
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}
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return b
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}
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// Encode takes a nalu unit and encodes it into an rtp packet and
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// writes to the io.Writer given in NewEncoder
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func (e *Encoder) Encode(payload []byte) error {
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pkt := Pkt{
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V: rtpVer, // version
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X: no, // header extension
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CC: no, // CSRC count
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M: no, // NOTE: need to check if this works (decoders should ignore this)
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PT: defaultPktType, // 33 for mpegts
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SN: e.nxtSeqNo(), // sequence number
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TS: e.nxtTimestamp(), // timestamp
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SSRC: e.ssrc, // source identifier
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Payload: payload,
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Padding: no,
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}
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_, err := e.dst.Write(pkt.Bytes(e.pktSpace[:defPktSize]))
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if err != nil {
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return err
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}
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e.tick()
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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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// nxtTimestamp gets the next timestamp
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func (e *Encoder) nxtTimestamp() uint32 {
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return uint32(e.clock.Seconds() * timestampFreq)
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}
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// nxtSeqNo gets the next rtp packet sequence number
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func (e *Encoder) nxtSeqNo() uint16 {
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e.seqNo++
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return e.seqNo - 1
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}
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