ISO standards developed by MPEG are made available in the form of textual specifications and whenever applicable also in the form of a reference software implementations of the standard and normative process to be performed. In the case of compressed audiovisual data, the reference software provides an implementation of the normative decoding process providing the values of output pixels or audio samples that all normative decoders are supposed to produce at their outputs. Reference encoders, whenever provided, are in general non-normative being only examples of possible encoding processes.
The textual specifications of ISO standards are available on the ISO web site together with the corresponding reference software parts. Different versions of the reference SW providing additional functionality or degrees of optimizations are also made available as direct additional ISO Standard Parts in the form of Technical Annexes (TA). In other cases, they take the form of open source projects and are made available to the public by the project promoters themselves outside of ISO (see for example the genie project).
In general, the encoding process is not normative and not specified as any encoding algorithm able to produce a syntactically conformant bitstream is conformant with the standard. This approach enables:
- The continuous progress of the encoding technology without the need to update the standard, but only the encoder implementations;
- The development of encoding solution addressing different requirements in terms of performance (speed/compression ratio) and resources consumption (high/low power).