RTCP (RTP Control Protocol) is the companion control channel that runs alongside RTP, carrying not media but feedback about it. Sender reports and receiver reports periodically exchange statistics — packets lost, jitter, round-trip time — and, crucially, the sender report pairs each stream's RTP timestamp with absolute NTP time, which is what lets a receiver lip-sync separate audio and video. RTCP also carries the extended feedback messages that drive congestion control (REMB, transport-cc) and request actions like keyframes. It uses only a small fraction of session bandwidth by design. If RTP is the conversation, RTCP is the two parties constantly confirming 'I got that, here's how it's going, here's the clock.'
The book · Volume 5 of 7
Audio for Video: A Complete Guide to Sound in Video Products: From Jitter Buffers and Lip Sync to Atmos, Quality Metrics, and Neural Codecs
RTCP carries the loss, jitter and timing feedback that drives both lip sync and bitrate adaptation, so a missing or misread report breaks both. This volume covers RTCP in depth with sender reports, NTP mapping, bandwidth estimation and jitter buffers, so you can read call statistics and fix problems from them. Written by Nikolay Sapunov, CEO at Fora Soft.
Using RTCP stats to debug call quality and unsure what the numbers are telling you?
Send us RTCP stats or captures from bad calls and we will interpret them, find the root cause and recommend concrete fixes. 250+ video products shipped since 2005.
