mirror of https://bitbucket.org/ausocean/av.git
107 lines
3.0 KiB
Go
107 lines
3.0 KiB
Go
/*
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NAME
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rtp.go - provides a data structure intended to encapsulate the properties
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of an rtp packet and also functions to allow manipulation of these packets.
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DESCRIPTION
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See Readme.md
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AUTHOR
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Saxon A. Nelson-Milton <saxon@ausocean.org>
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LICENSE
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rtp.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 [GNU licenses](http://www.gnu.org/licenses).
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*/
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/*
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See https://tools.ietf.org/html/rfc6184 and https://tools.ietf.org/html/rfc3550
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for rtp-h264 and rtp standards.
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*/
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package rtp
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const (
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rtpVer = 2
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headLen = 3 * 4
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defPayloadLen = 7 * 188
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defPktLen = headLen + defPayloadLen
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)
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// Pkt provides fields consistent with RFC3550 definition of an rtp packet
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// The padding indicator does not need to be set manually, only the padding length
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type Pkt struct {
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V byte // Version (currently 2)
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p byte // Padding indicator (0 => padding, 1 => padding)
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X byte // Extension header indicator
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CC byte // CSRC count
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M byte // Marker bit
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PT byte // Packet type
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SN uint16 // Synch number
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TS uint32 // Timestamp
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SSRC uint32 // Synchronisation source identifier
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Payload []byte // H264 Payload data
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Padding byte // No of bytes of padding
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}
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// Bytes provides a byte slice of the packet
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func (p *Pkt) Bytes(buf []byte) []byte {
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if buf == nil || len(buf) != defPktLen {
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buf = make([]byte, headLen, defPktLen)
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}
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buf = buf[:headLen]
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if p.V == 0 {
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p.V = rtpVer
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}
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if p.Padding > 0 {
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p.p = 1
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}
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if p.CC != 0 {
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panic("CC has been set to something other than 0 - this is not supported yet.")
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}
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if p.X != 0 {
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panic("rtp: X (extension header indicator) not 0, but extensiion headers not currently supported.")
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}
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if p.CC != 0 {
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panic("rtp: CC (CSRC count) not 0, but CSRC headers not yet supported.")
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}
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buf[0] = p.V<<6 | p.p<<5 | p.CC
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buf[1] = p.M<<7 | p.PT
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buf[2] = byte(p.SN >> 8)
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buf[3] = byte(p.SN)
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buf[4] = byte(p.TS >> 24)
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buf[5] = byte(p.TS >> 16)
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buf[6] = byte(p.TS >> 8)
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buf[7] = byte(p.TS)
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buf[8] = byte(p.SSRC >> 24)
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buf[9] = byte(p.SSRC >> 16)
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buf[10] = byte(p.SSRC >> 8)
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buf[11] = byte(p.SSRC)
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buf = append(buf, p.Payload...)
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// see https://tools.ietf.org/html/rfc3550 section 5.1 (padding). At end of
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// rtp packet, padding may exist, with the last octet being the length of the
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// padding including itself.
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if p.Padding != 0 {
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buf = buf[:cap(buf)]
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buf[len(buf)-1] = byte(p.Padding)
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}
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return buf
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}
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