Internet Protocols · Cluster
Real-Time Media
RTP, codecs, and jitter handling.
- 01 The RTP Fixed Header: Twelve Bytes That Carry a Media Stream What each field of the 12-byte RTP header means, why sequence numbers and timestamps are independent, and which failures the design accepts to stay small.
- 02 Reading Loss and Round-Trip Time from RTCP Sender and Receiver Reports How the fraction-lost, jitter, and LSR/DLSR fields are computed, why the arithmetic is fixed-point, and where the round-trip estimate breaks down.
- 03 Why RTP Timestamps Do Not Count Seconds RTP timestamps advance at the codec clock rate, which makes arithmetic modular and stream-relative; the rules that follow for wrap, comparison, and cross-stream sync.
- 04 Sizing and Adapting the Jitter Buffer How a playout buffer trades latency for concealment, the difference between a fixed and an adaptive delay target, and why the delay estimate must not follow every spike.
- 05 Opus: Two Codecs Behind One Payload Type SILK and CELT cover different frequency bands and latencies, and the hybrid mode that combines them explains most of Opus configuration decisions.
- 06 Fragmenting Encoded Frames to Fit the Path MTU Why a codec frame larger than a datagram needs RTP-level fragmentation, how the marker bit and timestamp stay shared, and what happens when one fragment is lost.
- 07 Early RTCP Feedback: Negative Acknowledgements, Picture Loss, and Transport Congestion How the feedback profiles let a receiver report loss in milliseconds instead of seconds, what each message type asks for, and the timing rules that keep them from flooding a session.
- 08 SRTP Key Derivation and Per-Packet IV Construction How one master key produces separate encryption, authentication, and salting keys, and why the packet index rather than the sequence number feeds the counter block.
- 09 Simulcast and Scalable Video: Choosing Which Layer to Send The difference between sending several independent encodings and sending one layered encoding, how receivers request a layer, and what switching costs in decoder state and bandwidth.
- 10 Mapping RTP Clocks to Wall Time for Cross-Stream Synchronization Sender reports tie an RTP timestamp to an NTP instant; using that correspondence to align audio and video exposes clock offset, drift, and the limits of the mapping.