Sustainability of Digital Formats
 Planning for Library of Congress Collections

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Identification and description

Full name	RealVideo, Version 10
Description	File format for video streaming. May be structured as "single stream," where the content is represented in one datastream, or as the scalable SureStream type, where a file contains multiple versions of content encoded at different data rates, with the selection of the stream for enduser presentation determined at delivery time. Streams may be encoded as constant bitrate, variable bitrate (encoded to provide target average bitrate), or for constant visual quality (producers may select a not-to-exceed instantaneous bitrate). In RealNetworks literature, version 9 is differentiated from version 10 only in terms of coding efficiency; this description applies to both.
Production phase	Generally a final-state (end-user delivery) format.
Relationship to other formats
Has earlier version	RealVideo 9, 8, and G2 SVT (Scalable Video Technology), not documented at this time.

Local use

LC experience or existing holdings	RealVideo, including versions earlier than 10, is used as streaming format for most video presented in American Memory, along with QuickTime. American Memory RealVideo has a data rate on the order of 20 kb/s, with a picture size of approximately 160x120 [less?], and a frame rate less than 15 fps.
LC preference	For file-based compressed video, considerations of quality and sustainability mean that MPEG-2 preferred over RealVideo; MPEG-1 and MPEG-4 may be acceptable. Uncompressed or losslessly compressed copies are preferred to compressed (for future development).

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 RealVideo and RealAudio, 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	Documentation for RealNetworks HelixProducer software indicates that embedded "Clip Information" (bibliographic or descriptive metadata) may include strings of 255 characters for title, author, and copyright owner identification; a string of 1,023 characters for keywords; a string of 64 kb for description; and a one-byte code for content rating (audience identification). Additional technical metadata is also embedded in RealMedia files.
External dependencies	Playback of surround sound requires multiple loudspeakers.
Technical protection considerations	A legal action in 2000 identified two technological protection measures in RealVideo. The first, "called the 'Secret Handshake' by RealNetworks, ensures that files hosted on a RealServer will only be sent to a RealPlayer. The Secret Handshake is an authentication sequence which only RealServers and RealPlayers know. By design, unless this authentication sequence takes place, the RealServer does not stream the content it holds. . . . By ensuring that RealMedia files hosted on a RealServer are streamed only to RealPlayers, RealNetworks can ensure that a second security measure, which RealNetworks calls the 'Copy Switch,' is given effect. The Copy Switch is a piece of data in all RealMedia files that contains the content owner's preference regarding whether or not the stream may be copied by end-users. RealPlayers are designed to read this Copy Switch and obey the content owner's wishes." (RealNetworks, Inc. v. Streambox, Inc.; United States District Court for the Western District of Washington; 2000 U.S. Dist., LEXIS 1889.)

Quality and functionality factors

Normal rendering for video	Good support.
Clarity (support for high image resolution)	Moderate to very good, given that RealVideo is a format for compression. RealNetworks literature suggests that RealVideo does not use block-based compression (as is the case, for example, for MPEG-2). The literature also cites three other quality factors: the option for Quality-Based Encoding, readiness for HDTV ("supports all HD formats and resolutions including 720p and 1080i"), and support for 60 field-per-second interlaced content. The quality of any given file will depend on the type and extent of compression, and the encoding option selected.
Fidelity (support for high audio resolution)	Moderate to very good, given that this is a format for compression. RealNetworks literature does not state this explicitely but presumably the same audio coding is available as for RealAudio. Outcome will depend on the type and extent of compression, and the encoding algorithm selected.
Support for multiple sound channels	Supported by RealAudio; presumed to be supported within RealVideo.
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	Note that streaming applications require an associated ram (RealMedia Metafile) file.
Filename Extension	rv	Note that streaming applications require an associated ram (RealMedia Metafile) file.
Filename Extension	rmvb	Variable bitrate. 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	video/vnd.rn-realvideo	From RealNetworks web page; this MIME type was associated with extension rv. 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

URLs

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Useful references

URLs
• http://docs.real.com/docs/rn/rv10/RV10_Tech_Overview.pdf. Promotional description of RealVideo 10 from RealNetworks, Inc.
• http://service.real.com/help/library/. Access point for documentation from RealNetworks, Inc., much of which pertains to production software, e.g., HelixProducer (see next entry).
• http://service.real.com/help/library/guides/helixproducer/htmfiles/toc_def.htm. Documentation of the HelixProducer product, which sheds light on many features of the RealVideo format.
• RealNetworks web page that (incidentally) lists Internet Media (MIME) Types (http://service.real.com/help/faq/rp8/configrp8win.html).
• RealNetworks, Inc. v. Streambox, Inc.; United States District Court for the Western District of Washington; 2000 U.S. Dist., LEXIS 1889 (http://www.law.uh.edu/faculty/cjoyce/copyright/release10/Real.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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