AMR File Storage Format
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.
What It Defines
Textual/storage envelope for AMR bitstreams: single-line magic (`#!AMR\n` for narrowband, `#!AMR-WB\n` for wideband) followed by consecutive codec frames with 1-byte frame headers (FT + quality bits). Used for voicemail files, MMS audio attachments, and mobile recordings.
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.
MMS is still widely used for group messaging (iMessage fallback on non-Apple devices), marketing images, and vCards. Understanding MM7 (application-to-MMSC API) is needed when integrating with carrier MMS gateways.
Every upload, download, attachment, and asset pipeline crosses these layers. Misunderstanding header vs envelope causes MIME spoofing bugs, parser differentials, and broken file validation. Start here before diving into individual format specs.