標準號：ISO/IEC TR 14496-24-2008
中文標準名稱：信息技術.視聽對象的編碼.第24部分:音頻與系統交互作用
英文標準名稱：Information technology - Coding of audio-visual objects - Part 24: Audio and systems interaction
標準類型：L71
發布日期：1999/12/31 12:00:00
實施日期：1999/12/31 12:00:00
中國標準分類號：L71
國際標準分類號：35.040
適用范圍：This part of ISO/IEC TR 14496 describes the desired joint behavior of MPEG-4 Systems (MPEG-4 FileFormat) and MPEG-4 Audio codecs. It is desired that MPEG-4 Audio encoders and decoders permit finitelength signals to be encoded to a file (particularly MPEG-4 files) and decoded again to obtain the identicalsignal, subject to codec distortions. This will allow the use of audio in systems implementations (particularlyMPEG-4 Systems), perhaps with other media such as video, in a deterministic fashion. Most importantly, thedecoded signal will have 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 artifacts);b) predictable synchronization between audio and other media such as video;c) correct behavior when performing random access as well as when starting at the beginning of astream;d) identical behavior when edits are applied in the raw domain and the encoded domain (again,excepting encoding artifacts).It is also required that there be predictable interoperability between encoders (as represented by files) anddecoders. There are two kinds of audio ‘offsets’ (or ‘delay’ in the context of transmission): those that resultfrom the encoding process, and those that result from the decoding process. This document is primarilyconcerned with the latter.These issues are resolved by the following:? The handling of composition time stamps for audio composition units is specified. Special care istaken in the case of compressed data, like HE-AAC coded audio, that can be decoded in a backwardcompatible fashion as well as in an enhanced fashion.? Examples are given that show how finite length signals can be encoded to an MPEG-4 file anddecoded again to obtain the identical signal, excepting codec distortions. Most importantly, thedecoded signal has nothing “extra” at the beginning or “missing” at the end.