http://www.rfc-editor.org/rfc/rfc7244.txt
RFC 7244: RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Synchronization Delay and Offset Metrics Reporting, H. Asaeda, Q. Wu, R. Huang2014-05-01T23:00:00-00:00This document defines two RTP Control Protocol (RTCP) Extended Report (XR) blocks that allow the reporting of initial synchronization delay and synchronization offset metrics for use in a range of RTP applications.