Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| 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. |
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| 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, |
| Contains | AAC_MP2, bitstream encoding |
| LC experience or existing holdings | None |
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| LC preference | 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. |
| Disclosure | Open standard. Developed by ISO technical program JTC 1/SC 29 (WG11), aka the Motion Pictures Expert Group (MPEG), Coding of audio, picture, multimedia and hypermedia information. |
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| Documentation | 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. |
| Adoption | See 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:
The next two elements are repeated (num_program_config_elements+1) times:
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| External dependencies | |
| Technical protection considerations |
| Sound | |
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| 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. |
| Tag | Value | Note |
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| Filename extension | aac |
From The File Extension Source. |
| Internet Media Type | See note. | None identified as of 2004-05-26. |
| General | |
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| History |
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