这两篇文章，可以直接去看；
https://www.jianshu.com/p/3a4d24a71091
https://blog.csdn.net/lincaig/article/details/81209895
《RTCP(一): RR–Receiver Reports 接收者报告》
https://blog.csdn.net/sweibd/article/details/79335748
《RTCP(二): SR–Sender Reports 接收者报告》
https://blog.csdn.net/sweibd/article/details/79344509