Format Description Categories
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Advanced Audio Coding (MPEG-2), Audio Data Interchange Format
Format Description Properties
- ID: fdd000112
- Short name: AAC_ADIF
- Content categories:
- Format Category:
- Other facets:
unitary, binary, sampled
- Last significant FDD update:
- Draft status: Full
Identification and description
||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.
||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.
||Generally used for final-state, end-user delivery.
|Relationship to other formats
MPEG-2 Video Encoding (H.262)
Advanced Audio Coding (MPEG-2)
|LC experience or existing holdings
||The Broadcast WAVE format (either version, WAVE_BWF_1 or WAVE_BWF_2), wrapping LPCM, is preferred as the archival master format for mono and stereo audio when reformatting analog sound recordings. Preferences for born-digital acquisitions have not been formally established as of this writing, but acceptable formats will certainly include WAVE, MP3, AAC, and possibly others.
||Open standard. 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 Motion Pictures Expert Group (MPEG).
||ISO/IEC 13818-7:2003. Information technology -- Generic coding of moving pictures and associated audio information -- Part 7: Advanced Audio Coding (AAC). See also MPEG-2.
| Licensing and patents
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).
|Technical protection considerations
Quality and functionality factors
|Fidelity (high audio resolution)
|Support for user-defined sounds, samples, and patches
|Functionality beyond normal rendering
File type signifiers
- ISO/IEC 13818-7:2003 Information technology -- Generic coding of moving pictures and associated audio information -- Part 7: Advanced Audio Coding (AAC).
- MPEG-2/MPEG-4 AAC (http://www.mp3-tech.org/aac.html). Page from MP3-tech.org.
- "MP3 and AAC Explained" is a 1999 article by Karlheinz Brandenburg, Fraunhofer Institute, Erlangen, Germany. It has good detail but with a focus on AAC_MP2. It is available in several locations and at least two forms.
- MP3 and AAC Explained (as PDF) (http://www.iis.fraunhofer.de/content/dam/iis/en/dokumente/AMM/Conference-Paper/AES17_mp3-and-AAC-explained-1.pdf). As published in proceedings of the 17th AES International Conference on High Quality Audio Coding, 1999, Sept 2-5.
- MP3 and AAC Explained (transcribed to HTML) (http://www.telos-systems.com/support/tech-talk/138-guest-papers/267-mp3-and-aac-explained). Transcription to HTML around 2013 indicates the article's classic status and continuing usefulness.
Monday, 10-Feb-2014 22:12:20 EST