Sustainability of Digital Formats: Planning for Library of Congress Collections

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RealAudio, RealAudio Codec

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name RealAudio, RealAudio Codec
Description Audio compression codec recommended by RealMedia for use when delivered bitrates are 128 kb/s or less, for lower bandwidth streaming.
Production phase Generally a final-state (end-user delivery) format.
Relationship to other formats
    Used by RealAudio_10, RealAudio, Version 10

Local use Explanation of format description terms

LC experience or existing holdings RealAudio, including versions earlier than 10 and using the RealAudio codec, is used as streaming format for most audio presented in American Memory, with a target data rate oriented to users with dial-up modems.
LC preference See RealAudio_10

Sustainability factors Explanation of format description terms

Disclosure See RealAudio_10
    Documentation See RealAudio_10
Adoption See RealAudio_10
    Licensing and patents See RealAudio_10
Transparency See RealAudio_10
Self-documentation See RealAudio_10
External dependencies See RealAudio_10
Technical protection considerations See RealAudio_10

Quality and functionality factors Explanation of format description terms

Sound
Normal rendering Good support
Fidelity (high audio resolution) Moderate; promotional literature says that this codec is "renowned for delivering near CD quality at 64 kbps."
Multiple channels Not investigated
Support for user-defined sounds, samples, and patches Not applicable

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension Not applicable. 

See RealAudio_10

Internet Media Type Not applicable. 

See RealAudio_10

Magic numbers Not applicable. 

See RealAudio_10

Microsoft FOURCC lpcJ and 14_4
Reported in Wikipedia for IS-54 VSELP (RealAudio 1)
Microsoft FOURCC 28_8
Reported in Wikipedia for G.728 LD-CELP (RealAudio 2)

Notes Explanation of format description terms

General A number of additional Microsoft FOURCC values are reported in the Wikipedia RealAudio article (consulted February 17, 2012). Some are reported in RealAudio_AAC, RealAudio_LL, and RealAudio_MC. Others include dnet: Dolby AC3 (RealAudio 3), sipr: Sipro Lab Telecom ACELP-NET (RealAudio 4/5), cook: G2/Cook Codec (RealAudio 6), and atrc: Sony ATRAC3 (RealAudio 8).
History  

Format specifications Explanation of format description terms


Useful references

URLs


Last Updated: 02/28/2017