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// Copyright 2020, Chef. All rights reserved.
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// https://github.com/q191201771/lal
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//
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// Use of this source code is governed by a MIT-style license
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// that can be found in the License file.
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//
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// Author: Chef (191201771@qq.com)
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package rtprtcp
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import (
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"errors"
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"github.com/q191201771/naza/pkg/bele"
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)
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// -----------------------------------
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// rfc3550 5.1 RTP Fixed Header Fields
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// -----------------------------------
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//
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// 0 1 2 3
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// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// |V=2|P|X| CC |M| PT | sequence number |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | timestamp |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | synchronization source (SSRC) identifier |
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// +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
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// | contributing source (CSRC) identifiers |
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// | .... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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var ErrRTP = errors.New("lal.rtp: fxxk")
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const (
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RTPFixedHeaderLength = 12
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)
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// rfc3984 5.2. Common Structure of the RTP Payload Format
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// Table 1. Summary of NAL unit types and their payload structures
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//
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// Type Packet Type name Section
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// ---------------------------------------------------------
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// 0 undefined -
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// 1-23 NAL unit Single NAL unit packet per H.264 5.6
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// 24 STAP-A Single-time aggregation packet 5.7.1
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// 25 STAP-B Single-time aggregation packet 5.7.1
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// 26 MTAP16 Multi-time aggregation packet 5.7.2
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// 27 MTAP24 Multi-time aggregation packet 5.7.2
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// 28 FU-A Fragmentation unit 5.8
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// 29 FU-B Fragmentation unit 5.8
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// 30-31 undefined -
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const (
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NALUTypeAVCSingleMax = 23
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NALUTypeAVCSTAPA = 24 // one packet, multiple nals
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NALUTypeAVCFUA = 28
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)
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const (
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NALUTypeHEVCFUA = 49
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)
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const (
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PositionTypeSingle uint8 = 1
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PositionTypeFUAStart uint8 = 2
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PositionTypeFUAMiddle uint8 = 3
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PositionTypeFUAEnd uint8 = 4
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PositionTypeSTAPA uint8 = 5
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)
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type RTPHeader struct {
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Version uint8 // 2b *
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Padding uint8 // 1b
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Extension uint8 // 1
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CsrcCount uint8 // 4b
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Mark uint8 // 1b *
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PacketType uint8 // 7b
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Seq uint16 // 16b **
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Timestamp uint32 // 32b ****
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Ssrc uint32 // 32b **** Synchronization source
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payloadOffset uint32
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}
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type RTPPacket struct {
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Header RTPHeader
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Raw []byte // 包含header内存
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positionType uint8
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}
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func ParseRTPPacket(b []byte) (h RTPHeader, err error) {
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if len(b) < RTPFixedHeaderLength {
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err = ErrRTP
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return
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}
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h.Version = b[0] >> 6
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h.Padding = (b[0] >> 5) & 0x1
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h.Extension = (b[0] >> 4) & 0x1
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h.CsrcCount = b[0] & 0xF
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h.Mark = b[1] >> 7
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h.PacketType = b[1] & 0x7F
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h.Seq = bele.BEUint16(b[2:])
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h.Timestamp = bele.BEUint32(b[4:])
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h.Ssrc = bele.BEUint32(b[8:])
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h.payloadOffset = RTPFixedHeaderLength
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return
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}
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// 比较序号的值，内部处理序号翻转问题，见单元测试中的例子
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func CompareSeq(a, b uint16) int {
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if a == b {
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return 0
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}
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if a > b {
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if a-b < 16384 {
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return 1
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}
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return -1
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}
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// must be a < b
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if b-a < 16384 {
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return -1
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}
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return 1
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}
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// a减b的值，内部处理序号翻转问题，如果a小于b，则返回负值，见单元测试中的例子
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func SubSeq(a, b uint16) int {
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if a == b {
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return 0
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}
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if a > b {
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d := a - b
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if d < 16384 {
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return int(d)
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}
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return int(d) - 65536
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}
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// must be a < b
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d := b - a
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if d < 16384 {
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return -int(d)
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}
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return 65536 - int(d)
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}
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