Sustainability of Digital Formats
 Planning for Library of Congress Collections

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Identification and description

Full name	MPEG-4 Version 2 file format with Advanced Audio Coding
Description	MPEG-4 Version 2 file format containing AAC encoded data.
Production phase	Generally used for final-state, end-user delivery.
Relationship to other formats
Subtype of	MP4_FF_2, MPEG-4 File Format, Version 2
May contain	AAC_MP4, Advanced Audio Coding, MPEG-4
May contain	AAC_MP4_LC, AAC (MPEG-4) Low Complexity Object
May contain	Additional audio, graphics, and scene graph stream types. Not documented at this time.

Local use

LC experience or existing holdings	None
LC preference	General preference for recorded sound is WAVE_LCPM. For compressed sound, MP4_FF_2_AAC is acceptable.

Sustainability factors

Disclosure	See MP4_FF_2
Documentation	See MP4_FF_2 and AAC_MP4.
Adoption	See MP4_FF_2 and AAC_MP4.
Licensing and patent claims	See MP4_FF_2 and AAC_MP4.
Transparency	See AAC_MP4.
Self-documentation	See MP4_FF_2 and AAC_MP4.
External dependencies	See AAC_MP4.
Technical protection considerations	See MP4_FF_2.

Quality and functionality factors

Normal rendering	Good support.
Fidelity (support for high audio resolution)	See AAC_MP4.
Support for multiple sound channels	See AAC_MP4.
Support for downloadable or user-defined sounds, samples, and patches	See AAC_MP4.
Functionality beyond normal rendering	See AAC_MP4.

File type signifiers

Tag type	Value	Note
Filename Extension		See MP4_FF_2 and AAC_MP4.
Internet Media Type		See MP4_FF_2.

Notes

General
History

Format specifications

URLs
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• ISO/IEC 14496-1:2001 Information technology -- Coding of audio-visual objects -- Part 1: Systems
  • ISO/IEC 14496-1:2001/Amd 1:2001 Extended BIFS
  • ISO/IEC 14496-1:2001/Amd 4:2003 SL extensions and AFX streams
• ISO/IEC 14496-3:2001 Information technology -- Coding of audio-visual objects -- Part 3: Audio
  • ISO/IEC 14496-3:2001/Cor 1:2002
  • ISO/IEC 14496-3:2001/Amd 1:2003 Bandwidth extension
• ISO/IEC 14496-12:2004 Information technology -- Coding of audio-visual objects -- Part 12: ISO base media file format
• ISO/IEC 14496-14:2003 Information technology -- Coding of audio-visual objects -- Part 14: MP4 file format

Useful references

URLs
• MPEG-2/MPEG-4 AAC page from MP3-tech.org (www.mp3-tech.org/aac.html)
• "MP3 and AAC Explained," by Karlheinz Brandenburg, Fraunhofer Institute, Erlangen, Germany (focus on AAC_MP2; http://www.aes.org/publications/downloadDocument.cfm?accessID=14703162000122117).
• Site for users of the format (http://www.m4a.com/)

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