ISO/IEC 23094-4:2022

Overview

ISO/IEC 23094-4:2022 - "Information technology - General video coding - Part 4: Conformance and reference software for essential video coding" defines the conformance test methods and reference software for Essential Video Coding (EVC). The standard specifies the tests, bitstream test suites and a reference software decoder/encoder intended to verify whether bitstreams and decoders meet the normative requirements given in ISO/IEC 23094-1:2020. It establishes how to determine if an encoder’s output is a conforming bitstream and whether a decoder’s capabilities match the profiles and levels defined for EVC.

Key topics and requirements

• Bitstream conformance
  • Use of the reference software decoder to check that candidate bitstreams do not trigger errors or non-conformance messages.
  • Parsing full bitstreams and validating syntax elements; complementary verification may be required for HRD-related constraints (Annexes C, D, E).
• Decoder conformance
  • Two conformance classes: output order conformance (decoded pictures and sample values match reference) and output timing conformance (decoded samples produced at the rates and times specified in Annex C of ISO/IEC 23094‑1).
  • Decoder capabilities specify which bitstreams a decoder must be able to decode and reconstruct.
• Test artifacts and procedure
  • Conformance bitstream packages (electronic annex) contain: bitstream, decoded pictures or hashes, short description, and trace files.
  • Static tests (sample-value comparison or hashes) and dynamic tests (timing, HRD - CPB/DPB verification).
  • Recommendations for robust decoder behavior (e.g., recovery after bitstream loss, concealment).
• Reference software and ETM
  • Reference encoder/decoder usage and an ETM (test model of EVC) repository are described for reproducible testing.

Practical applications and users

• Codec developers and encoder vendors use ISO/IEC 23094-4 to validate that encoded bitstreams conform to EVC profiles and levels.
• Decoder implementers and silicon vendors apply the tests to demonstrate output order and timing conformance, and HRD compliance.
• Test laboratories and certification bodies run the supplied test suites and reference software for compliance verification.
• System integrators and streaming platform engineers rely on conformance testing to ensure interoperability between encoders, network delivery, and decoders.

Related standards

• ISO/IEC 23094-1:2020 - Essential video coding (syntax, semantics, decoder model)
• Normative references in ISO/IEC 23094-4 include programming and interface standards such as ISO/IEC 9899 (C) and POSIX (ISO/IEC/IEEE 9945) for reference software portability.

For test materials and electronic annex: https://standards.iso.org/iso-iec/23094/-4/ed-1/en/