Sustainability of Digital Formats
 Planning for Library of Congress Collections

Format Description Categories >> Browse Alphabetical List>> Back

Identification and description

Full name	RealAudio, Version 10
Description	File format for 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 codec)
Has subtype	RealAudio_AAC, (AAC codec)
Has subtype	RealAudio_LL, (lossless codec)
Has subtype	RealAudio_MC, (multichannel codec)
May contain	RealAudio codec, not separately documented
May contain	AAC, codec
May contain	RealAudio lossless codec, not separately documented
May contain	RealAudio multichannel codec, not separately documented

Local use

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

Disclosure	Proprietary format with little public documentation, although licenses for certain classes of developers may provide access to source code.
Documentation	Documentation
Adoption	Very widely adopted for streaming web content and other online applications.
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 to build tools.
Self-documentation	[Embedded bibligraphic 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

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

Tag	Value	Note
Filename extension	rm [for audio?]	Note that streaming applications require an associated ram (RealMedia Metafile) file.
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

General
History

Format specifications

• See Disclosure under Sustainability factors.

Useful references

URLs

• http://docs.real.com/docs/rn/datasheet/RA_10_Datasheet_S203.pdf (http://docs.real.com/docs/rn/datasheet/RA_10_Datasheet_S203.pdf). . Promotional description of RealAudio 10 from RealNetworks, Inc.
• http://service.real.com/help/library/ (http://service.real.com/help/library/). . Access point for documentation from RealNetworks, Inc., much of which pertains to production software.
• http://service.real.com/help/library/guides/helixproducer/htmfiles/app_code.htm (http://service.real.com/help/library/guides/helixproducer/htmfiles/app_code.htm). . Discussion of codecs for RealAudio, apparently for version 8. Some of this information may be valid for RealAudio codecs.
• RealNetworks web page (http://service.real.com/help/faq/rp8/configrp8win.html). that (incidentally) lists Internet Media (MIME) Types .
• IANA MIME Media Types (http://www.iana.org/assignments/media-types/). official page; RealMedia not listed .
• Gary Kessler's File Signatures Table (http://www.garykessler.net/library/file_sigs.html). , source for magic numbers .
• The File Extension Source (http://filext.com/). , for file extensions and magic numbers .