Sustainability of Digital Formats: Planning for Library of Congress Collections

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RealAudio, Version 10

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name RealAudio, Version 10
Description Proprietary file format for streaming audio. Provides for four different codecs; see Relationships to Other Formats, below.
Production phase Generally a final-state (end-user delivery) format.
Relationship to other formats
    Has subtype RealAudio_RA, RealAudio, RealAudio Codec
    Has subtype RealAudio_AAC, RealAudio, AAC Codec
    Has subtype RealAudio_LL, RealAudio, Lossless Codec
    Has subtype RealAudio_MC, RealAudio, Multichannel Codec
    May contain RealAudio codec, not separately documented
    May contain AAC, Advanced Audio Coding (MPEG-2). (codec)
    May contain RealAudio lossless codec, not separately documented
    May contain RealAudio multichannel codec, not separately documented

Local use Explanation of format description terms

LC experience or existing holdings RealAudio, including versions earlier than 10, is used as a streaming format for most sound recordings presented in American Memory, with a target data rate oriented to users with dial-up modems.
LC preference Considerations of quality and sustainability mean that WAVE_LPCM is preferred over RealAudio; considerations of sustainability mean that MP3 is preferred. Although no Library preference for media-independent surround sound has been established at this writing, formats including MPEG-4 with AAC audio encoding and WMA (Windows Media Audio) may be preferred to RealAudio_MC (multichannel codec).

Sustainability factors Explanation of format description terms

Disclosure Proprietary format with little public documentation, although licenses for certain classes of developers may provide access to source code.
    Documentation Limited documentation
Adoption Widely adopted for streaming web content and other online applications, starting in the mid-1990s. As of March 2012, the Wikipedia page for RealAudio notes that although used widely by radio stations for streaming audio in the past, use has become less common in recent years. In particular, the BBC dropped use from its primary website in 2009, and from the BBC World Service in 2011.
    Licensing and patents Licensing for RealAudio and RealVideo, and for related production and delivery tools, is described at https://helixcommunity.org/content/licenses, an entity of RealNetworks, Inc. Licensing includes open source and research and development arrangements that provide access to the source code for the codecs.
Transparency Depends upon algorithms and tools to read; will require sophistication and documentation to build tools.
Self-documentation Embedded bibliographic or descriptive metadata is included in online examples, e.g., title, artist, genre. This writer could not find documentation as of April 2004; RealAudio may share metadata structure with RealVideo.
External dependencies Playback of surround sound requires multiple loudspeakers.
Technical protection considerations RealAudio likely to share technical protection devices with RealVideo.

Quality and functionality factors Explanation of format description terms

Moving Image
Normal rendering Good support.
Functionality beyond normal rendering A sequence of Web pages can be synchronized for display with the playback of streaming media in a RealMedia player when HTML-page URLs are embedded in a RealMedia clip.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension rm
For RealMedia file. See HomeRecording.com for discussion of audio-only .rm vs .ra files.
Filename extension ra
Note that streaming applications require an associated ram (RealMedia Metafile) file.
Internet Media Type application/vnd.rn-realmedia
From RealNetworks web page; this MIME type was associated with extension rm. No examples found in IANA MIME Media Types.
Internet Media Type audio/vnd.rn-realaudio
From RealNetworks web page; this MIME type was associated with extension ra and ram. No examples found in IANA MIME Media Types.
Magic numbers Hex: 2E 52 4D 46
ASCII: .RMF
From Gary Kessler's File Signatures Table.
Magic numbers Hex: 2E 52 4D 46 00 00 00 12 00
ASCII: .RMF
From The File Extension Source.

Notes Explanation of format description terms

General  
History  

Format specifications Explanation of format description terms


Useful references

URLs


Last Updated: 02/21/2017