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Macromedia Flash SWF File Format, Version 7

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Macromedia Flash SWF File Format, Version 7

Delivers vector graphics (especially animations) and other data types, including "bitmapped" video, over the Internet to the Macromedia Flash Player. Commentators describe the technology as "non-native" to the Web. Very simple playback (with a repeat loop) is controlled by a timeline; interactive examples (even very simple ones) use both a timeline and ActionScript, a scripting language similar to JavaScript. ActionScripts may reference objects within the SWF file or resources external to it, e.g., Macromedia FLV video files.

SWF files are typically derived from a FLA file (Macromedia Flash Project File); they may also be produced in other ways using third-party software. SWF files may be combined with a runtime version of the Flash player, resulting in a file type called projector. Windows versions of projector files are executables with an exe extension.

The swf extension was originally used for files played by Macromedia's Shockwave browser plug-in; see Notes for additional history information.

In 2005, Adobe purchased Macromedia and a branding changeover began. The documentation for the Flash (SWF) format, version 8, was disseminated from the Adobe Web site but still carried the Macromedia brand on the cover sheet.

Production phase Used for final-state, end-user delivery.
Relationship to other formats
    Has earlier version Macromedia Flash (SWF) Versions 3, 4, 5, and 6, not documented here
    Has later version SWF_8, Macromedia Flash SWF File Format, Version 8
    May contain Sorenson encoded video.1
    May contain Screen Video Bitstream Format (ScreenVideo), not documented here.
    May contain Raw PCM sampled audio content, not documented here.
    May contain ADPCM, Adaptive Delta Pulse Code Modulation
    May contain MP3_ENC, MP3
    May contain Nellymoser Asao (speech compression) audio content, not documented here.
    Used by QuickTime, QuickTime File Format
    Other FLA, Macromedia Flash FLA Project File Format.. Explanatory note: SWF files are typically derived from ("save as") a FLA file.

Local use Explanation of format description terms

LC experience or existing holdings Seven SWF motion picture and two SWF interactive titles were collected by the Motion Picture, Broadcasting, and Recorded Sound Division in 2002. Version number unknown at this writing.
LC preference None established at this time. Potential challenges to the preservation of SWF files are discussed in Richard Entlich's article "Flash in the Pan or Around for the Long Haul?". The compilers of this document seek advice regarding preservation preferences: SWF, FLA, a projector version, or is it advisable to archive all three?

Sustainability factors Explanation of format description terms

Disclosure Fully documented. Developed by Macromedia, Inc., now owned by Adobe Systems.
    Documentation The specification for version 8 (Macromedia Flash (SWF) and Flash Video (FLV) File Format Specification, Version 8, n.d., copyright notice 2005) includes documentation for versions 6 and 7. (Consulted in February 2007.) Prior to the announcement of version 8, The Macromedia Flash SWF File Format Specification, Version 7, n.d.(copyright notice 2002-2003). was available at
Adoption Adoption is diminishing, particularly for mobile device users. Adobe posted the following on their blogon November 11, 2011: "HTML5 is now universally supported on major mobile devices, in some cases exclusively. This makes HTML5 the best solution for creating and deploying content in the browser across mobile platforms... Our future work with Flash on mobile devices will be focused on enabling Flash developers to package native apps with Adobe AIR for all the major app stores. We will no longer continue to develop Flash Player in the browser to work with new mobile device configurations (chipset, browser, OS version, etc.) following the upcoming release of Flash Player 11.1 for Android and BlackBerry PlayBook. We will of course continue to provide critical bug fixes and security updates for existing device configurations. We will also allow our source code licensees to continue working on and release their own implementations."
    Licensing and patents Adobe offers the specification and the right to build tools to produce SWF files (in the current version, no longer version 7) via a free license.
Transparency Not transparent; proprietary binary format.
Self-documentation None accessible via the player. Tags within the file identify data types, e.g., the particular sound encoding used. Regarding descriptive data, Macromedia offers search engine application engineers a software development kit that extracts any indexable information from SWF files that producers may have incorporated. The challenge of indexing Flash and similar content is discussed in a special report from the Search Engine Strategies conference in Boston, March 4-6, 2003. Until late 2006, this report was available at
External dependencies None.
Technical protection considerations None known to the compilers of this document.

Quality and functionality factors Explanation of format description terms

Moving Image
Normal rendering Good support
Clarity (high image resolution) Vector content is scalable and thus free of most clarity issues. "Bitmapped" video in SWF files may be compressed in two ways. One option is a Sorenson codec,1 which apparently extends to large picture sizes. Another option is the Screen Video Bitstream Format, optimized for "captures of computer screens in motion," described on page 15 of the SWF specification formerly available at The video quality in these encodings is expected to range from good to very good.
Functionality beyond normal rendering ActionScript permits a wide range of interactive options, and scripts may call on both internal and external resources.
Normal rendering Good support
Fidelity (high audio resolution) The SWF specification limits uncompressed audio to 44 kHz sampling and 16 bit words, thus providing very good fidelity. The use of compression will reduce fidelity in accord with the specific encoding and settings selected.
Multiple channels Stereo only.
Support for user-defined sounds, samples, and patches None.
Functionality beyond normal rendering ActionScript permits a wide range of interactive options, and scripts may call on both internal and external resources.

File type signifiers Explanation of format description terms

Tag Value Note
Filename extension swf
From the Flash SWF Specification (version 7), p. 9. The Wikipedia article on Adobe Flash (consulted February 5, 2007) includes a list of file types (with extensions) associated with the Flash family.
Internet Media Type application/x-shockwave-flash
From the Flash SWF Specification, version 7, p. 9.
Internet Media Type application/x-shockwave-flash2-preview
Selected from The File Extension Source
Magic numbers Hex: 46 57 53
For uncompressed files; from the Flash SWF Specification, version 7, p. 10. The next byte in the file provides the version number; Hex 07 (0x07) for version 7.
Magic numbers Hex: 43 57 53
For files compressed with ZLIB; from the Flash SWF Specification, version 7, p. 10. The next byte in the file provides the version number; Hex 07 (0x07) for version 7.

Notes Explanation of format description terms

General In principle, SWF files could be used for static vector graphics but there appears to be little or no practice of doing this. VG files can be used for animations but here again there appears to be little or no practice and even SVG advocates state that Macromedia's powerful authoring software gives SWF the edge.

From Richard Entlich's article "Flash in the Pan or Around for the Long Haul?": "Flash traces its origins to a browser plug-in called FutureSplash, originally produced by a company called FutureWave, but purchased by Macromedia in 1996 and renamed Flash. At the time, Macromedia offered a Web plug-in called Shockwave that decoded several of its multimedia products, including Flash. Thus the MIME type for Flash is application/x-shockwave-flash and the file extension for binary Flash files is 'swf' for Shockwave Flash. Ultimately, Macromedia moved away from handling multiple content types with a single plug-in. Today, the Shockwave plug-in is only used to play content produced by Macromedia's Director, an older tool originally for developing interactive CD-ROM content but now also used for Web animation. The plug-in that plays back Flash content is called Flash Player. However, the term Shockwave Flash is still widely used (even by Macromedia), and is the source of much understandable confusion.

"Over the years, Flash has grown in power and popularity. It drew attention early for its ability to create animations that were fairly compact and fast-loading. Subsequently, Flash has become more sophisticated, with a powerful scripting language (called ActionScript) similar to JavaScript, and the ability to render a wide range of interactive Web site content. Recent versions of Flash can incorporate sound and video. Even though it is a vector graphic tool, Flash can incorporate raster graphics (i.e., bitmaps) . . . . Flash is prized by many developers for its ability to provide a visually rich and highly interactive user experience not easily achievable with other technologies."

Format specifications Explanation of format description terms

Useful references


1 Flash documentation for version 7 does not state a number for "their" version of Sorenson but describes the codec as a variant of ITU-T (International Telecommunications Union) recommendation H.263 (See MPEG-4_V). In early 2006, one of Sorenson's compression applications to produce content for Flash offered the Sorenson_3 codec, described by experts as a variant of ITU-T H.264 (MPEG-4_AVC). By late 2006, Sorenson offered new compression applications with other outputs.

Last Updated: Thursday, 31-Oct-2013 10:59:55 EDT