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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 "time"
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// 通过收到的rtp包和rtcp sr包，产生rtcp rr包
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type RRProducer struct {
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senderSSRC uint32
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mediaSSRC uint32
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clockRate int
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maxSeq int32
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baseSeq int32
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cycles uint32
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received uint32
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extendedSeq uint32
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transit int64
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jitter uint32
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expectedPrior uint32
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receivedPrior uint32
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}
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func NewRRProducer(clockRate int) *RRProducer {
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return &RRProducer{
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clockRate: clockRate,
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baseSeq: -1,
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maxSeq: -1,
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transit: -1,
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}
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}
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// 每次收到rtp包，都将seq序号传入这个函数
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func (r *RRProducer) FeedRTPPacket(seq uint16) {
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r.received++
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if r.baseSeq == -1 {
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r.baseSeq = int32(seq)
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}
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if r.maxSeq == -1 {
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r.maxSeq = int32(seq)
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} else {
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if CompareSeq(seq, uint16(r.maxSeq)) > 0 {
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if seq < uint16(r.maxSeq) {
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r.cycles++
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}
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r.maxSeq = int32(seq)
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}
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}
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r.extendedSeq = (r.cycles << 16) | uint32(r.maxSeq)
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}
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// 收到sr包时，产生rr包
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//
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// @param lsr: 从sr包中获取，见func SR.GetMiddleNTP
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// @return: rr包的二进制数据
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//
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func (r *RRProducer) Produce(lsr uint32) []byte {
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if r.baseSeq == -1 {
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return nil
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}
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var lost uint32
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expected := r.extendedSeq - uint32(r.baseSeq) + 1
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if expected < r.received {
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lost = 0
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} else {
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lost = expected - r.received
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}
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var fraction uint8
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expectedInterval := expected - r.expectedPrior
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r.expectedPrior = expected
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receivedInterval := r.received - r.receivedPrior
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r.receivedPrior = r.received
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lostInterval := expectedInterval - receivedInterval
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if expectedInterval == 0 || lostInterval <= 0 {
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fraction = 0
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} else {
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fraction = uint8((lostInterval << 8) / expectedInterval)
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}
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var rr RR
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rr.senderSSRC = r.senderSSRC
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rr.mediaSSRC = r.mediaSSRC
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rr.fraction = fraction
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rr.lost = lost
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rr.cycles = uint16(r.cycles)
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rr.extendedSeq = r.extendedSeq
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rr.jitter = r.getJitter()
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rr.lsr = lsr
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return rr.Pack()
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}
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// @param timestamp 当前收到的rtp包头中的时间戳
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func (r *RRProducer) updateJitter(timestamp uint32) {
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// rfc3550 6.4.1 SR: Sender Report RTCP Packet
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// rfc3550 A.8 Estimating the Interarrival Jitter
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// 当前收到rtp包的本地物理时间
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arrival := int64(time.Now().UnixNano() / 1e6)
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// 物理时间和包时间的差值，都换算成包时间戳格式
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transit := arrival*(int64(r.clockRate)/1000) - int64(timestamp)
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// 第一次跳过
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if r.transit == -1 {
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r.transit = transit
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return
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}
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// 这次差值，和上一次差值相减
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d := transit - r.transit
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if d < 0 {
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d = -d
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}
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// 一种设置jitter的方式
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// set: r.jitter += (float32(1)/16) * (d - r.jitter)
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// get: return r.jitter
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//
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// 另外一种方式
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// 对应的get: return r.jitter >> 4
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// 注意，右边的计算结果肯定是正数
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r.jitter = r.jitter + uint32(d) - ((r.jitter + 8) >> 4)
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}
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func (r *RRProducer) getJitter() uint32 {
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return r.jitter >> 4
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}
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