Sustainability of Digital Formats: Planning for Library of Congress Collections

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RealVideo, Version 10

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

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 Explanation of format description terms

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 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, although streaming media capabilities are increasingly important, the need for proprietary solutions such as Real Video has reduced, given the emergence of openly documented alternatives. For example, MPEG-4_AVC (aka H.264), was adopted by Apple for its iPod/iPad devices, and is now widely used. Although those developing HTML5 would like to require browsers to support one streaming video format, no obvious candidate has emerged, in part because H.264 must be licensed. See http://en.wikipedia.org/wiki/HTML5_video. A new option is VP8, acquired by Google with On2 Technologies, openly described in November 2011 at http://www.ietf.org/rfc/rfc6386.txt, and made available under a royalty-free license.
    Licensing and patents 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 and documentation 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 speakers.
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 Explanation of format description terms

Moving Image
Normal rendering Good support.
Clarity (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.
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
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 Explanation of format description terms

General  
History  

Format specifications Explanation of format description terms


Useful references

URLs


Last Updated: Tuesday, 21-Feb-2017 07:56:36 EST