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Format Description Properties
• ID: fdd000051
• Short name: RealAudio_10
• Content categories: sound
• Format category: bitstream encoding, file format
• Last significant update: 2004-05-03
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 | |
| Supertype of | RealAudio_RA (RealAudio codec) |
| Supertype of | RealAudio_AAC (AAC codec) |
| Supertype of | RealAudio_LL (lossless codec) |
| Supertype of | 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 | Various promotional and instructional documents from RealNetworks, Inc.; see list in Useful References below. |
| Adoption | Very widely adopted for streaming web content and other online applications. |
| Licensing and patent claims | 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 (sound)
| Normal rendering | Good support. |
| Fidelity (support for high audio resolution) | Moderate to excellent, depending upon the codec selected; for mono and stereo recordings, the lossless codec offers the highest fidelity while the AAC codec will provide the best result for compressed sound. |
| Support for multiple channels | All codecs support mono and stereo; the multichannel codec supports 5 or 6 channels (5.1 audio). Presumably the multichannel codec can be used for multiple channel sound not intended to represent aural space. |
| Support for downloadable or user-defined sounds, samples, and patches | Not applicable |
| Functionality beyond normal video 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 type | 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
Format specifications
URLs
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Useful references
URLs
• 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/. 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. Discussion of codecs for RealAudio, apparently for version 8. Some of this information may be valid for RealAudio codecs.
• RealNetworks web page that (incidentally) lists Internet Media (MIME) Types (http://service.real.com/help/faq/rp8/configrp8win.html).
• IANA MIME Media Types official page; RealMedia not listed (http://www.iana.org/assignments/media-types/).
• Gary Kessler's File Signatures Table, source for magic numbers (http://www.garykessler.net/library/file_sigs.html).
• The File Extension Source, for file extensions and magic numbers (http://filext.com/).
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Last Updated: Wednesday, 07-Mar-2007 12:40:18 EST
