TNO Netherlands TNO Netherlands TNO Netherlands TNO Netherlands TNO Netherlands CWI Netherlands Universidad Politecnica de Valencia Universidad Politecnica de Valencia This document gives information on an RTCP Packet Type and RTCP XR Block Type including associated SDP parameters for inter-destination media synchronization (IDMS). The RTCP XR Block Type, registered with IANA based on an ETSI specification, is used to collect media play- out information from participants in a group playing-out (watching, listening, etc.) a specific RTP media stream. The RTCP packet type specified by this document is used to distribute a summary of the collected information so that the participants can synchronize play- out. Typical applications for IDMS are social TV, shared service control (i.e. applications where two or more geographically separated users are watching a media stream together), distance learning, network quiz shows, multi-playing online games, etc.