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Advanced Audio Coding (MPEG-2), Audio Data Interchange Format

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Table of Contents
Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Formal name (from MPEG-2 documentation that specifies both the AAC_MP2 bitstream and the ADIF file structure.): ISO/IEC 13818-7:2003. Information technology -- Generic coding of moving pictures and associated audio information -- Part 7: Advanced Audio Coding (AAC). Common names: AAC and ADIF. In 1999, MPEG-2 Part 7 was updated and included in the MPEG-4 family of standards and became known as MPEG-4 Part 3, MPEG-4 Audio or ISO/IEC 14496-3:1999.
Description Bitstream encoding and file format designed for efficient distribution of sound files over moderate bandwidth connections; may be used at higher data rates for better fidelity. ADIF stands for Audio Data Interchange Format and consists of a brief header that precedes AAC data in a file. Note that the compression approach in AAC_MP2 (used in this format) was subsequently refined as AAC_MP4, which requires a different decoder.
Production phase Generally used for final-state, end-user delivery.
Relationship to other formats
    Subtype of MPEG-2, MPEG-2 Video Encoding (H.262)
    Contains AAC_MP2, Advanced Audio Coding (MPEG-2)

Local use Explanation of format description terms

LC experience or existing holdings None
LC preference Not applicable. See the Recommended Formats Statement for more information.

Sustainability factors Explanation of format description terms

Disclosure Open standard. Originally developed through ISO technical program JTC 1/SC 29 for coding of audio, picture, multimedia and hypermedia information by Working Group 11 (WG11) aka the Moving Picture Experts Group (MPEG). In 1999, MPEG-2 Part 7 was updated and included in the MPEG-4 family of standards and became known as MPEG-4 Part 3, MPEG-4 Audio or ISO/IEC 14496-3:1999.
    Documentation ISO/IEC 13818-7:2003. Information technology -- Generic coding of moving pictures and associated audio information -- Part 7: Advanced Audio Coding (AAC). This document has been withdrawn. See also MPEG-2.
Adoption AAC_ADIF not in current use. See also AAC_MP2.
    Licensing and patents See AAC_MP2.
Transparency See AAC_MP2.
Self-documentation

According to the Audio Coding Wiki, which is no longer available as of June, 2010, the ADIF format actually is just one header at the beginning of the AAC file. And the rest of the data are consecutive raw data blocks. This file format is meant for simple local storing purposes unlike ADTS or LATM which are meant for streaming AAC. The ADIF header is made up of the following tagged elements; the field size in bits is provided in the parentheses, followed by a comment:

  • adif_id/ (32). Always has value "ADIF"
  • copyright_id_present (1).
  • copyright_id (72). Only present if copyright_id_present has value 1
  • original_copy (1).
  • home (1).
  • bitstream_type (1). 0 for CBR; 1 for VBR
  • bitrate (23). For CBR: bitrate; for VBR: peak bitrate; 0 means unknown
  • num_program_config_elements (4).

The next two elements are repeated (num_program_config_elements+1) times:

  • buffer_fullness (20). Only if bitstream_type has value 0
  • program_config_element (VAR).
External dependencies  
Technical protection considerations  

Quality and functionality factors Explanation of format description terms

Sound
Normal rendering Good support.
Fidelity (high audio resolution) See AAC_MP2.
Multiple channels See AAC_MP2.
Support for user-defined sounds, samples, and patches See AAC_MP2.
Functionality beyond normal rendering See AAC_MP2.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension aac
 From The File Extension Source.
Internet Media Type audio/aac
 From IANA Media Types
Pronom PUID See related format.  See AAC_MP2
Wikidata Title ID See related format.  See AAC_MP2

Notes Explanation of format description terms

General According to Wikipedia, "AAC audio data was first packaged in a file for the MPEG-2 standard using Audio Data Interchange Format (ADIF), consisting of a single header followed by the raw AAC audio data blocks. However, if the data is to be streamed within an MPEG-2 transport stream, a self-synchronizing format called an Audio Data Transport Stream (ADTS) is used, consisting of a series of frames, each frame having a header followed by the AAC audio data. This file and streaming-based format are defined in MPEG-2 Part 7, but are only considered informative by MPEG-4, so an MPEG-4 decoder does not need to support either format. These containers, as well as a raw AAC stream, may bear the .aac file extension. MPEG-4 Part 3 also defines its own self-synchronizing format called a Low Overhead Audio Stream (LOAS) that encapsulates not only AAC, but any MPEG-4 audio compression scheme such as TwinVQ and ALS. This format is what was defined for use in DVB transport streams when encoders use either SBR or parametric stereo AAC extensions. However, it is restricted to only a single non-multiplexed AAC stream. This format is also referred to as a Low Overhead Audio Transport Multiplex (LATM), which is just an interleaved multiple stream version of a LOAS."
History

In 1999, MPEG-2 Part 7 was updated and included in the MPEG-4 family of standards and became known as MPEG-4 Part 3, MPEG-4 Audio or ISO/IEC 14496-3:1999.


Format specifications Explanation of format description terms


Useful references

URLs


Last Updated: 04/08/2022

 
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