ISO/IEC 14496-34:2025

Overview

ISO/IEC 14496-34:2025 defines a Syntactic Description Language (SDL) for describing the structure of binary data used in audio‑visual coding and related systems. The standard specifies the plain‑text representation, lexical and syntactic rules, and the semantic interpretation of SDL specifications. It also clarifies how ambiguous or undefined constructs are to be treated (invalid specification vs undefined behaviour). The SDL is optimized for describing bit‑level formats and is explicitly not a general‑purpose programming language.

Key topics and technical scope

The document covers a comprehensive set of language and format topics useful for precise binary format descriptions:

• Language fundamentals: character set, whitespace, identifiers, comments, keywords, operators, precedence and associativity.
• Literals and values: binary, hexadecimal, string, integer, decimal and floating‑point literal forms; logic values; value coercion and limits.
• Endianness and bitstream examples: rules for representing multibyte values and illustrative bitstream fragments.
• Elementary data types: constant and variable length bit fields (direct and indirect), alignment, look‑ahead, reserved/legacy fields, strings.
• Composite data types: classes, base/derived classes, abstract classes, polymorphism and expandable classes.
• Arrays and multidimensional arrays: fixed, partial and implicit arrays, alignment considerations.
• Computed variables and expressions: parsed vs computed scope, evaluation rules and use in data definitions.
• Syntactic flow control: conditionals, loops and other constructs to describe conditional, repeating or optional structures.
• Semantics and limits: rules for what constitutes a valid SDL specification and handling of undefined behaviour.

Practical applications and users

ISO/IEC 14496-34:2025 is directly applicable wherever precise, unambiguous binary format descriptions are required:

• Codec and encoder/decoder developers - define and implement bitstream parsing and generation for audio‑visual codecs.
• Protocol and container implementers - describe packet, header and payload structures to ensure interoperability.
• Test labs and conformance suites - generate, validate and compare bitstreams against authoritative SDL specifications.
• Tooling vendors - build parsers, format validators, documentation generators and test vector creators from SDL.
• Standards authors and system integrators - document format details and reduce misinterpretation between implementers.

Benefits include improved interoperability, repeatable conformance testing, clearer documentation of bit‑level structures and easier implementation of robust parsers.

Related standards

• ISO/IEC 14496 series (coding of audio‑visual objects) - SDL is Part 34 within this series and complements other parts that define codecs, containers and metadata.

Keywords: ISO/IEC 14496-34, Syntactic Description Language, SDL, binary data structure, bitstream format, audio‑visual coding, format specification, parser, interoperability, conformance testing.