ISO/IEC JTC 1/SC 29/WG 11 - Coding of moving pictures and audio

This document describes the desired joint behaviour of MPEG-4 Systems (MPEG-4 File Format) and MPEG-4 Audio codecs. It is desired that MPEG-4 Audio encoders and decoders permit finite length signals to be encoded to a file (particularly MPEG-4 files) and decoded again to obtain the identical signal, subject to codec distortions. This enables the use of audio in systems implementations (particularly MPEG-4 Systems), perhaps with other media such as video, in a deterministic fashion. Most importantly, the decoded signal has nothing “extra” at the beginning or “missing” at the end. This permits: a) an exact "round trip" from raw audio to encoded file back to raw audio (excepting encoding artefacts); b) predictable synchronization between audio and other media such as video; c) correct behaviour when performing random access as well as when starting at the beginning of a stream; d) identical behaviour when edits are applied in the raw domain and the encoded domain (excepting encoding artefacts). It is also expected that there be predictable interoperability between encoders (as represented by files) and decoders. There are two kinds of audio "offsets" (or "delay" in the context of transmission): those that are result from the encoding process, and those that are result from the decoding process. This document is primarily concerned with the latter. These issues are resolved by the following: - The handling of composition time stamps for audio composition units is specified. Special care is taken in the case of compressed data, like HE-AAC coded audio, that can be decoded in a backward compatible fashion as well as in an enhanced fashion. - Examples are given that show how a finite length signals can be encoded to an MPEG-4 file and decoded again to obtain the identical signal, excepting codec distortions. Most importantly, the decoded signal has nothing “extra” at the beginning or “missing” at the end.

This document specifies the interfaces of a video decoding engine as well as the operations related to elementary streams and metadata that can be performed by this video decoding engine. To support those operations, this document also specifies SEI messages when necessary for certain video codecs.

This document specifies MPEG media transport (MMT) technologies, which include a single encapsulation format, delivery protocols and signalling messages for transport and delivery of multimedia data over heterogeneous packet-switched networks for multimedia services. Types of packet-switched networks supported by this document include bidirectional networks such as Internet Protocol (IP) networks and unidirectional networks such as digital broadcast networks (which may or may not use the IP). The technologies specified by this document belong to one of three functional areas of MMT: media processing unit (MPU) format, signalling messages and delivery protocol. The MPU format specifies the “mpuf” branded ISO-based media file format (ISOBMFF) encapsulating both timed and non-timed media contents. The MPU format is a self-contained ISOBMFF structure enabling independent consumption of media data, which hides codec-specific details from the delivery function. The signalling functional area specifies the formats of signalling messages carrying information for managing media content delivery and consumption, e.g. specific media locations and delivery configuration of media contents. The delivery functional area specifies the payload formats that are independent of media and codec types, which allow fragmentation and aggregation of contents encapsulated as specified by this document for delivery using packet-switched oriented transport protocols. The delivery functional area also provides an application layer transport protocol that allows for advanced delivery of media contents.