RTCP Feedback Message and Request Mechanism for Frame-level Acknowledgement

This document describes a mechanism for signaling which video frames have been received and decoded by a remote peer. It comprises an RTCP feedback message and an RTP header extension used to request said feedback. One of the main use cases for this data is to implement various forms of Long Term Reference (LTR) reference structures. Additionally, the mechanism provides a way for receivers to request resynchronization frames that reference acknowledged frames, enabling efficient recovery from partial or full frame loss without requiring a full keyframe.