RTP Payload Format for AMR / AMR-WB
VoLTE and IMS carry AMR over RTP per RFC 4867 — not as `.amr` files. CMR bits and octet-align vs bandwidth-efficient modes cause real interoperability bugs between carriers.
What It Defines
Defines bandwidth-efficient and octet-aligned RTP payload formats for AMR-NB and AMR-WB speech frames, including interleaving, CRC, and codec-mode request (CMR) header bits. The wire-format counterpart to `.amr` file storage.
Canonical (Normative)
Convenient (Practical)
The canonical publication point for finalized RFCs. If a protocol is standardized as an RFC, the RFC Editor text is the normative final reference. Published by the IETF, IRTF, IAB, and independent stream.
Related Specs
AMR-NB is the fallback voice codec for pre-VoLTE mobile networks and many carrier voicemail systems. The `#!AMR` file header and RFC 4867 RTP framing are distinct from AMR-WB.
AMR-WB is mandatory for VoLTE — every LTE voice call uses it. Understanding rate adaptation and the AMR payload format (RFC 4867) is essential for mobile VoIP and operator codec policy.
The AMR file header is a minimal envelope pattern — one magic line then framed payloads. Required when parsing `.amr`/`.awb` attachments from carrier APIs or MMS gateways.
RTP carries all real-time media: VoIP, WebRTC, live video, and video conferencing. Understanding SSRC demultiplexing, jitter buffers, and RTCP feedback loops is essential for any media application.
3GP is the standard container for mobile-recorded video/voice messages, MMS media, and legacy carrier content. Shares ISO BMFF box structure with MP4 but restricted codec set.