Multicodec

Multicodec is a standard within the multiformats ecosystem that provides a centralized registry of codes used to identify codecs and protocols for data payloads. Each entry in the registry assigns a unique numeric code to a specific encoding or format, enabling data to be self-describing and easily interpreted across different systems.

In practice, a multicodec value is encoded as a varint (variable-length integer) that precedes the data it describes. This prefix allows software to determine how to parse the subsequent bytes without prior knowledge of the format. The registry is designed to be extensible, so new codes can be added as formats evolve while preserving backward compatibility with existing data.

Multicodec plays a key role in content addressing and data interchange. It is used by Content Identifiers (CIDs) and various multiformats to declare the encoding of the payload, facilitating interoperability among networks and applications such as IPFS, Filecoin, and related projects. Software that supports multiple formats relies on the multicodec prefix to select the appropriate parser and handling logic.

The multicodec registry is maintained by the Multiformats community and published as part of the broader multiformats project. Codes are proposed and reviewed through a governance process, ensuring clear descriptions, status, and deprecation guidance. Implementations exist in multiple languages and are used by developers to support robust cross-platform data exchange.