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SWF
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Small Web Format (SWF)
Filename extension
.swf
Internet media type
application/vnd.adobe.flash.movie,[1] application/x-shockwave-flash[2][3]
Magic numberCWS,FWS[4] or ZWS[5]
Developed byFutureWave Software,
later taken over by Macromedia and
Adobe Systems
Type of formatVector graphic animation
Container forAdobe Flash (formerly Macromedia Flash and FutureSplash), sometimes labeled Shockwave Flash Object.

SWF (/ˈswɪf/)[6] is a defunct Adobe Flash file format that is used for multimedia, vector graphics and ActionScript.[7]

Originating with FutureWave Software, then transferred to Macromedia, and then coming under the control of Adobe, SWF files can contain animations or applets of varying degrees of interactivity and function. They may also occur in programs, commonly browser games, using ActionScript.

Programmers can generate SWF files from within several Adobe products, including Flash, Flash Builder (an IDE), Adobe Animate (a rename of Adobe Flash since 2016), and After Effects, as well as through MXMLC, a command-line application compiler which forms part of the freely-available Flex SDK. Although Adobe Illustrator can generate SWF format files through its "export" function, it cannot open or edit them. Other than using Adobe products, one can build SWFs with open-source Motion-Twin ActionScript 2 Compiler (MTASC), the open-source Ming library and the free-software suite SWFTools. Various other third-party programs can also produce files in this format, such as Multimedia Fusion 2, Captivate and SWiSH Max.

The term "SWF" originated as an abbreviation for ShockWave Flash.[8] This usage was changed to the backronym Small Web Format to eliminate confusion with a different technology, Shockwave, from which SWF derived.[9][10] There is no official resolution to the initialism "SWF" by Adobe.[11]

Adobe declared its Flash player EOL on December 31, 2020. On January 12, 2021, it pushed an update to its Flash player that blocked all Flash content from running.[12]

History

[edit]

The small company FutureWave Software originally defined the file format with one primary objective: to create small files for displaying entertaining animations.[13] The idea involved a format which player software could run on any system and which would work with slower network connections. FutureWave released FutureSplash Animator in May 1996. In December 1996 Macromedia acquired FutureWave and FutureSplash Animator became Macromedia Flash 1.0.

The original naming of SWF came out of Macromedia's desire to capitalize on the well-known Macromedia Shockwave brand; Macromedia Director produced Shockwave files for the end user, so the files created by their newer Flash product tried to capitalize on the already established brand. As Flash became more popular than Shockwave itself, this branding decision became more of a liability, so the format started to be referred to as simply SWF.[8]

Adobe acquired Macromedia in 2005.[14]

On May 1, 2008, Adobe dropped its licensing restrictions on the SWF format specifications, as part of the Open Screen Project. However, Rob Savoye, a member of the Gnash development team, has pointed to some parts of the Flash format which remain closed.[15] On July 1, 2008, Adobe released code to Google and Yahoo, which allowed their search engines to crawl and index SWF files.[16]

Description

[edit]

The main graphical primitive in SWF is the path, which is a chain of segments of primitive types, ranging from lines to splines or Bézier curves. Additional primitives like rectangles, ellipses, and even text can be built from these. The graphical elements in SWF are thus fairly similar to SVG and MPEG-4 BIFS. SWF also uses display lists and allows naming and reusing previously defined components.[17]

The binary stream format SWF uses is fairly similar to QuickTime atoms, with a tag, length and payload – an organization that makes it very easy for (older) players to skip contents they don't support.[17]

Originally limited to presenting vector-based objects and images in a simple sequential manner, the format in its later versions allows audio (since Flash 3) and video (since Flash 6).

Adobe introduced a new, low-level 3D API in version 11 of the Flash Player. Initially codenamed Molehill, the official name given to this API was ultimately Stage3D. It was intended to be an equivalent of OpenGL or Direct3D.[18]: 9  In Stage3D shaders are expressed in a low-level language called Adobe Graphics Assembly Language (AGAL).[18]: 57 [19]

Adoption

[edit]
See also: Adobe Flash § Players, and Adobe Flash § Animation Tools

Adobe makes available plugins, such as Adobe Flash Player and Adobe Integrated Runtime, to play SWF files in web browsers on many desktop operating systems, including Microsoft Windows, Mac OS X, and Linux on the x86 architecture and ARM architecture (ChromeOS only).

GNU has started developing a free software SWF player called Gnash under the GNU General Public License (GPL). Despite being a declared high-priority GNU project, funding for Gnash was fairly limited.[20] Another player is the LGPL-licensed Swfdec. Lightspark is a continuation of Gnash supporting more recent SWF versions.[20]

Adobe has incorporated SWF playback and authoring in other product and technologies of theirs, including in Adobe Shockwave, which renders more complex documents.[17] SWF can also be embedded in PDF files; these are viewable with Adobe Reader 9 or later.[21] InDesign CS6 can also produce some limited forms of SWF animations directly.[22]

Sony PlayStation Portable consoles can play limited SWF files in Sony's web browser, beginning with firmware version 2.71. Both the Nintendo Wii[23] and the Sony PS3[24] consoles can run SWF files through their web browsers.

Scaleform GFx is a commercial alternative SWF player that features full hardware acceleration using the GPU and has high conformance up to Flash 8 and AS2. Scaleform GFx is licensed as a game middleware solution and used by many PC and console 3D games for user interfaces, HUDs, mini games, and video playback.[citation needed]

The newer 3D features of SWF have been seen as an alternative to WebGL, with a spurt of 3D engines like Papervision3D,[25][26][27] Away3D,[25][28][29] Sandy 3D,[25][30] and Alternativa 3D targeting 3D SWF.[31] Although some of these projects started around 2005, until Flash Player 10 however they had no support of GPU acceleration, and even in that version of the Flash Player, shaders could be used for same materials, but vertex information still had to be processed on the CPU (using BSP trees etc.)[31] After version 11 of the Flash Player added the new Stage3D low-level API, some but not all of these projects migrated to the new API. One that did migrate was Away3D, version 4.[32]

Based on an independent study conducted by Millward Brown and published by Adobe, in 2010, over 99% of desktop web browsers in the "mature markets" (defined as United States, Canada, United Kingdom, France, Germany, Japan, Australia, and New Zealand) had a SWF plugin installed, with around 90% having the latest version of the Flash Player.[33]

Due to the increasing popularity of HTML5 for games and animations, as well as the numerous security holes that had plagued Adobe's SWF player, Adobe declared its Flash player EOL on December 31, 2020. On January 12, 2021, it pushed an update to its Flash player that blocked all Flash content from running.

Published specifications

[edit]

Adobe makes available a partial specification of SWF,[34] most recently updated in January 2013 to reflect changes in SWF version 19.[35] SWF versions have been decoupled from Flash player versions after Flash 10. Afterwards the version number of the SWF progressed rapidly; SWF version 19 corresponds to the new features added in Flash Player 11.6.[36] Flash Player 14 uses SWF version 25.[37]

In 2008, the specifications document was criticized by Rob Savoye, the lead developer of the Gnash project, as missing "huge amounts" of information needed to completely implement SWF, omitting specifications for RTMP and Sorenson Spark.[15] The RTMP specification[38] was released publicly in June 2009.[citation needed] The Sorenson Spark codec is not Adobe's property.

Licensing

[edit]

Until May 1, 2008, implementing software that plays SWF was disallowed by the specification's license.[39] On that date, as part of its Open Screen Project, Adobe dropped all such restrictions on the SWF and FLV formats.[40]

Implementing software which creates SWF files has always been permitted, on the condition that the resulting files render "error free in the latest publicly available version of Adobe Flash Player."[41]

[edit]

Other formats related to SWF authoring in the Adobe tool chain remain without a public specification. One example is FLA, which is the editable version of SWF used by Adobe's Flash, but not by other Adobe tools that can also output SWF, albeit with fewer features.[42]

Extension Explanation
.abc Actionscript bytecode used by the Actionscript Virtual Machine AVM (Flash 8 and prior), and AVM2 (Flash 9 or later).
.amf Action Message commands for transacting with a FMS.
.as ActionScript source code in simple source files. FLA files can also contain Actionscript code directly, but separate external .as files often emerge for structural reasons, or to expose the code to versioning applications.
.asc Server-Side ActionScript, which is used to develop efficient and flexible client-server Macromedia Flash Communication Server MX applications.
.aso Cache files used during Flash development, containing compiled ActionScript byte code. An ASO file is recreated when a change in its corresponding class files is detected. Occasionally the Flash IDE does not recognize that a recompile is necessary, and these cache files must be deleted manually. They are located in %USERPROFILE%\Local Settings\Application Data\Macromedia\Flash8\en\Configuration\Classes\aso on Win32 / Flash8.
.f4a Adobe suffix for iTunes M4A files that contain only audio streams.[43]
.f4b Adobe suffix for iTunes M4B audiobook files.[43]
.f4f MP4 atom-ized fragmented files. Containing FLV packets.
.f4m XML manifest files. Containing base64 FLV onMetaData headers for an Adobe version of bit rate control HTTP Live Streaming.
.f4p Adobe suffix for media encrypted with the Adobe Access digital rights management scheme which is based on the same protection scheme that their RTMP protocol uses.[43]
.f4v Similar to iTunes M4V files which are based on MP4 and can be played back by Flash Player 9 Update 3 and above. F4V file format is second container format for Flash video and it differs from FLV file format. It is based on the ISO base media file format.[44][43]
.fla Source material for the Flash application. Flash authoring software can edit FLA files and compile them into .swf files. The Flash source file format is currently a binary file format based on the Microsoft Compound File Format. In Flash Pro CS5, the fla file format is a zip container of an XML-based project structure.
.flp XML files used to reference all the document files contained in a Flash Project. Flash Projects allow the user to group multiple, related files together to assist in Flash project organization, compilation and build.
.flv Flash Video files, as created by Adobe Flash, ffmpeg, Sorenson Squeeze, or On2 Flix. The audio and video data within FLV files are encoded in the same way as they are within SWF files.
.fxg Unified xml file format being developed by Adobe for Flex, Flash, Photoshop and other applications.
.jsfl Adds functionality in the Flash Authoring environment; they contain JavaScript code and access the Flash JavaScript API.
.mxml Used in conjunction with ActionScript files (and .css files), and offer a markup-language-style syntax (like HTML) for designing the GUI in Flex. Each MXML file creates a new class that extends the class of the root tag, and adds the nested tags as children (if they are descendants of UIComponent) or members of the class.
.sol Adobe Flash Player container to hold Local Shared Objects (data stored on the system running the Flash player).
.spl FutureSplash Animator documents.
.swc Container for distributing components; they contain a compiled clip, the component's ActionScript class file, and other files that describe the component.
.swd Temporary debugging files used during Flash development. Once finished developing a Flash project these files are not needed and can be removed.
.swf Completed, compiled and published files that cannot be edited with Adobe Flash. However, several non-Adobe '.swf decompilers' exist (like that of Sothink) to convert SWF back to the FLA format,[45] or to the more recent Apache Flex format.[46] Attempting to import .swf files using Flash allows it to retrieve some assets from the .swf, but not all.[47]
.swt 'Templatized' forms of .swf files, used by Macromedia Generator. It is also Adobe Dreamweaver's Flash template file extension.[48]
.xfl XML-based project files that are equivalent to the binary .fla format. Flash authoring software uses XFL as an exchange format in Flash CS4. It imports XFL files that are exported from InDesign and AfterEffects. In Flash Pro CS5, the xfl file is a key file which opens the "uncompressed FLA" file, which is a hierarchy of folders containing XML and binary files.

See also

[edit]
Adobe Flash
Other

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

SWF

View on Grokipedia
from Grokipedia
A sovereign wealth fund (SWF) is a state-owned or entity that manages a country's surplus financial assets, such as revenues from exports, , or fiscal surpluses, to generate long-term economic benefits for current and future generations. These funds typically invest in a diversified portfolio of assets, including equities, , , , and , both domestically and internationally, with the primary goals of wealth preservation, economic stabilization, and . Sovereign wealth funds emerged prominently in the mid-20th century, with the first modern example being Kuwait's Reserve Fund established in 1953 to manage oil revenues, followed by rapid growth in the and due to booms in resource-rich nations. By 2025, there are over 90 active SWFs worldwide, including recent initiatives such as the U.S. national established via in February 2025, collectively managing more than $13 trillion in (AUM) as of 2025, representing a significant portion of global institutional investment capital. The largest SWFs include Norway's Government Pension Fund Global, with approximately $2 trillion in AUM as of 2025, primarily funded by oil and gas revenues and invested ethically to promote ; China's , valued at around $1.3 trillion and focused on diversifying foreign reserves; and the Abu Dhabi Investment Authority, estimated at over $1 trillion and known for its opaque but influential global investments. SWFs are classified into several types based on their objectives: stabilization funds to buffer against economic volatility, savings funds for , development funds to support domestic infrastructure and economic growth, and reserve investment corporations to enhance returns on central bank reserves. Governance practices vary, but many adhere to international standards like the Santiago Principles, a voluntary code established in 2008 by the International Forum of Sovereign Wealth Funds to promote transparency, accountability, and prudent investment policies, addressing concerns over political influence and market distortions. These funds play a crucial role in global finance, often acting as long-term investors that stabilize markets during crises, such as through increased equity purchases during the 2008 financial meltdown and the downturn, while also facing scrutiny for potential geopolitical risks in their investment strategies.

Overview

Definition and Characteristics

The SWF (Small Web Format) file format is a compact binary format designed for delivering animations, , interactive content, and multimedia elements such as audio and video over the web. It was originally developed as Shockwave Flash but renamed to emphasize its efficiency for web applications. Key characteristics of SWF include support for using paths defined by straight lines and quadratic Bézier curves, which allow for resolution-independent rendering similar to SVG but in a binary structure. The format embeds bitmaps for raster images, enables scripting for user interactivity, and applies compression techniques such as zlib (introduced in version 6) or LZMA (from version 13) to minimize file sizes while maintaining a rectangular bounding box for display areas. These features facilitate smooth playback of frame-based animations, gradients, and mixed media without requiring server-side processing. The SWF file header, spanning the initial 8 bytes, provides essential metadata for playback. It begins with a 3-byte —'FWS' for uncompressed files or 'CWS' for zlib-compressed ones (with 'ZWS' for LZMA in later versions)—followed by a 1-byte version number ranging from 1 to 32 in final implementations. Subsequent fields include a 4-byte unsigned for total file length, a RECT structure specifying frame size in twips (1/20th of a ), a 2-byte in 8.8 fixed-point format (typically 1 to 655.35 frames per second), and a 2-byte unsigned for the frame count. Unlike text-based formats such as XML or , SWF's binary encoding uses bit-packing and tags for efficient storage, resulting in significantly smaller files that enabled rapid loading on early internet connections during the and . This design prioritizes delivery speed and low bandwidth usage, making it suitable for browser-embedded content.

Primary Uses

SWF files were primarily designed for delivering compact, interactive content over the web, serving as the output format for animations, vector illustrations, and embedded audio/video playback created with authoring tools like . These applications leveraged the format's efficiency in handling , which maintain quality across different screen sizes, to create engaging web-based experiences such as animated banners and illustrative diagrams. A key strength of SWF lay in its support for , enabling developers to incorporate user input through and keyboard events, form submissions, and of content. This facilitated the creation of simple browser-based , interactive advertisements that responded to user actions, and e-learning modules or product demonstrations where content updated in real-time based on user interactions. For instance, scripting allowed for handling events like button clicks to submit or load external resources, making SWF ideal for rich internet applications that communicated with servers. SWF files were typically exported from and embedded in web pages using tags such as <embed> or <object>, allowing playback via the Flash Player plugin in browsers. They could also be compiled into standalone files, bundling the runtime for offline execution without requiring a browser. In niche applications, SWF supported delivery through Flash Lite for pre-iOS devices, enabling lightweight animations and video streaming on feature phones and early smartphones. Additionally, via the runtime, SWF-based content powered desktop applications, interactive experiences as native executables for platforms like Windows and macOS. Server-side generation of SWF for dynamic was possible using libraries like Ming, allowing programmatic creation of customized animations from languages such as .

History

Early Development

FutureWave Software was founded in January 1993 in , , by Jonathan Gay, Charlie Jackson, and Michelle Welsh, initially to develop graphics and animation software for pen-based personal digital assistants (PDAs) such as the and GO Corporation's PenPoint operating system. The company's first product, SmartSketch, was a vector drawing application released in 1995, but FutureWave soon pivoted toward web-compatible animation tools amid growing interest in online multimedia. In May 1996, FutureWave released FutureSplash Animator version 1.0, an authoring tool designed for creating compact 2D vector-based animations suitable for the early web. This initial version provided basic vector drawing tools, support for tweening to generate smooth transitions between keyframes, and export capabilities to the .spl —a binary structure optimized for small file sizes and playback over dial-up connections supporting 8-bit (256-color) graphics at a default of 12 frames per second. Accompanying the software was the FutureSplash Player, a plugin for (and later ), which enabled animations to stream progressively in web browsers, allowing immediate playback without waiting for complete downloads—a critical innovation for the bandwidth-constrained of the mid-1990s, where speeds rarely exceeded 28.8 kbps. The binary efficiency of the .spl format laid the groundwork for web animation standards by prioritizing lightweight, over pixel-heavy alternatives like GIFs. By late 1996, FutureSplash had gained early adopters including and , demonstrating its potential for interactive web content. In December 1996, Macromedia acquired , integrating FutureSplash Animator into its portfolio and rebranding it as Macromedia Flash 1.0 shortly thereafter.

Macromedia and Adobe Periods

In 1997, Macromedia acquired FutureWave Software and rebranded FutureSplash Animator as Macromedia Flash 1.0, establishing the SWF (Small Web Format) as the core runtime file format for delivering vector-based animations and interactive content via web browsers. This rebranding positioned Flash as a lightweight alternative to heavier multimedia tools, with the SWF format enabling compact files suitable for dial-up internet speeds of the era. By May 1998, Flash 3.0 introduced key enhancements including alpha transparency for layered graphics and licensed MP3 audio compression, significantly improving visual and sound capabilities for web designers. During the Macromedia era from 1997 to 2005, Flash integrated seamlessly with Macromedia's Director software to support the broader Shockwave platform, allowing developers to embed SWF content within more complex multimedia projects for enhanced interactivity on the web. Versions 4 through 8 expanded functionality progressively: Flash 4 (1999) introduced the initial programming language for basic scripting; Flash 5 (2000) formalized 1.0 with object-oriented features; and Flash MX (version 6, 2002) advanced developer tools with 2.0, timeline effects, and the Sorenson Spark video codec for embedded streaming video, while adding options like support. Flash 8 (2005) further refined video handling with the On2 VP6 codec and bitmap filters, solidifying Flash's role in rich media production. These updates were accompanied by ongoing security patches addressing vulnerabilities such as buffer overflows in earlier players, with Macromedia issuing regular advisories to mitigate remote code execution risks. Following Adobe's acquisition of Macromedia in 2005, Flash development accelerated, with versions 9 through 11 (corresponding to SWF versions 9 through 11 from 2006 to 2011) introducing advanced multimedia support tailored for evolving web and mobile ecosystems. Flash Player 10 (2008) added Pixel Bender for GPU-accelerated effects, while version 10.1 (2010) enabled H.264 video codec integration for high-quality streaming and , alongside expanded 3D graphics via libraries. Adobe also advanced mobile deployment through Flash Lite, a lightweight variant for devices like early smartphones, allowing SWF playback on non-PC platforms. By this period, Flash achieved peak browser penetration exceeding 95% globally, powering interactive advertisements, games, and video sites. Key milestones included Flash CS3 (2007, version 9) with improved IDE tools and the 2006 launch of Adobe Flex, a framework for building data-driven rich internet applications (RIAs) using MXML and , which streamlined enterprise development. Adobe continued proactive security measures, releasing monthly patches for critical flaws like type confusion vulnerabilities in these versions to counter exploitation attempts.

Discontinuation

In July 2017, announced the end-of-life for Flash Player, scheduling the cessation of updates and distribution by the end of , primarily due to persistent vulnerabilities—such as zero-day exploits including CVE-2015-5119 and CVE-2019-7845 that enabled —and the growing adoption of open web standards like HTML5. This decision followed years of Flash's dominance in web multimedia during the , marking a shift away from proprietary plugins toward more secure, native browser technologies. The official end-of-life arrived on December 31, 2020, after which blocked all Flash content from running in the player starting January 12, 2021, with major browsers like Chrome, , and Edge enforcing similar restrictions to prevent security risks. To support legacy access for non-malicious purposes, released a final offline installer version of Flash Player, allowing limited playback on isolated systems without connectivity. Following discontinuation, enterprises accelerated migrations of Flash-based applications and content to and , leveraging tools like Animate's export features and third-party converters to ensure compatibility across modern browsers and devices. For cultural preservation, community efforts such as the project emerged, archiving over 100,000 Flash games and animations to safeguard web history from . As of 2025, Adobe provides no official support for SWF or Flash Player, rendering it incompatible with current web ecosystems, though open-source emulators like Ruffle—a Rust-based Flash Player implementation—enable partial browser-based playback of verified, non-malicious content through WebAssembly.

Technical Specifications

File Structure and Tags

The SWF file format is organized as a binary stream beginning with a fixed header followed by a sequence of variable-length tags that define the multimedia content, concluding with an End tag to mark the file's termination. The header spans 8 to 12 bytes and includes essential metadata: a 3-byte signature ("FWS" for uncompressed files or "CWS" for compressed), a 1-byte version number, a 4-byte file length (indicating the total size in bytes, with the uncompressed size for CWS files), a RECT structure for frame size, a 2-byte frame rate (in 8.8 fixed-point format), and a 2-byte frame count. The version number in the header determines the availability of certain tags, though the core structure remains consistent across versions. For compressed SWF files (identified by the "CWS" ), zlib compression is applied to the body starting immediately after the initial 8 bytes (, version, and file length), enabling smaller file sizes while preserving the tag-based organization upon decompression. Following the header, the file consists of a series of tags, each representing a discrete instruction or definition for rendering elements such as , animations, or media; these tags are processed sequentially until the End tag (type 0) is encountered. There are over 80 defined tag types in the format, allowing for the modular construction of complex movies through combinations of definition tags (which create reusable assets) and control tags (which place or manipulate them on the display list). Each tag begins with a RECORDHEADER: a 2-byte short header combining a 10-bit tag ID (indicating the type) and a 6-bit length (for up to 62 bytes), or a long header extending to a 4-byte length field for larger payloads, ensuring efficient of variable-sized . Tags define core movie elements, including vector shapes via tags like DefineShape (which specifies bounds, fill styles such as solid colors or gradients, and line styles with widths and colors), bitmaps imported as or through DefineBits or DefineBitsJPEG2, embedded fonts using DefineFont with shapes derived from outlines, and audio via DefineSound for formats like or ADPCM. Control tags such as PlaceObject position characters (reusable assets) on the display list with transformation matrices, while ShowFrame advances the to render the current frame. Record formats within tags employ bit-packing for compactness, exemplified by the RECT structure used for bounds and dimensions: it starts with a 5-bit field specifying NBits (the number of bits per coordinate, typically 0-15), followed by four signed bit fields (Xmin, Xmax, Ymin, Ymax) each of NBits length, measured in (where 1 twip equals 1/20th of a ) to provide sub- precision. This bit-packed approach extends to other records, such as matrices for scaling and (using fixed-point values for , scaling, and skew) and shape records that outline paths with straight lines, curves, or style changes, enabling the efficient encoding of without redundant data. The following table summarizes selected major tag types central to the file structure, highlighting their roles in defining and controlling content:
Tag IDTag NamePurpose
0EndTerminates the sequence of tags.
1ShowFrameRenders the current display list as a frame in the .
2DefineShapeDefines a basic vector shape with bounds, fills, and lines.
4PlaceObjectPlaces a defined character on the display list with position and matrix.
6DefineBitsImports and defines a character.
10DefineFontDefines font glyphs using shape tables for text rendering.
14DefineSoundDefines an event-based clip (e.g., or ADPCM data).
20DefineBitsLosslessDefines a lossless (ZLIB-compressed PNG-like data).
21DefineBitsJPEG2Defines a with separate alpha channel.
22DefineShape2Extends shape definition with edge capabilities.
26PlaceObject2Enhanced placement with color transforms and ratios.
These tags collectively form the backbone of SWF , where definition tags must precede their usage in control tags to build the movie's visual and audio hierarchy.

ActionScript Integration

serves as the primary for embedding interactivity and logic within SWF files, enabling dynamic behaviors such as user input handling, timeline control, and content manipulation. It operates through two main virtual machines: AVM1 for earlier versions and AVM2 for modern implementations, with scripts compiled into for efficient execution by the Flash Player runtime. The language evolved across versions to support increasing complexity. ActionScript version 1.0, introduced with Flash 4 in 1999, provided simple actions for basic operations like playback control and variable manipulation. Version 2.0, released in 2003 with Flash MX 2004, introduced elements, including classes and inheritance, while maintaining compatibility with AVM1. ActionScript version 3.0, launched in 2006, adheres to standards for enhanced performance and scalability, compiling source code to ActionScript Byte Code (ABC) stored within DoABC tags for AVM2 execution. These versions allow developers to attach scripts directly to timeline elements, buttons, or frames, facilitating responsive applications without altering the core file structure. Scripts are embedded via specific tags that integrate code into the SWF's tag stream. In AVM1 (for versions 1.0 and 2.0), actions are placed in DefineButton or PlaceObject tags, utilizing a stack-based model with opcodes like ActionPush for data loading onto the stack and ActionGotoFrame for navigation. AVM2 (for version 3.0 and later) employs a register-based bytecode system with structured elements such as traits for class definitions and methods for function implementation, also embedded in DoABC tags; DoAction tags provide additional placement for frame-level scripts. This embedding ensures scripts execute in context with visual and interactive elements defined elsewhere in the file. Execution occurs as the player runtime processes tags sequentially during playback, interpreting on frame loads or events. Event handlers, such as onClipEvent for mouse clicks, key presses, or load events, trigger scripts in response to user interactions or timeline milestones, processed via control flows like ShowFrame tags. To enforce , the runtime applies a sandbox model that isolates SWF content by domain, restricting cross-domain access—such as loading external data or scripts—unless explicitly allowed via policy files, preventing unauthorized resource sharing between untrusted sources. Central to ActionScript's functionality are core concepts like MovieClip objects, which represent interactive sprites or symbols with their own timelines, enabling programmatic control over animation states and child elements. Display lists manage the hierarchical layering and rendering of visual objects, allowing scripts to add, remove, or reorder items for complex scenes. A representative example is the command _root.gotoAndPlay(1), which targets the main timeline to jump to frame 1 and resume playback, illustrating timeline manipulation in practice. These mechanisms prioritize efficient, event-driven interactivity while adhering to the SWF's sequential processing model.

Versions and Evolution

The SWF file format originated with in 1996, introducing basic , simple shapes, text, and flat display lists using tags such as PlaceObject, RemoveObject, DefineShape, and DefineBits for uncompressed audio and bitmaps, enabling rudimentary animations. Version 2, released in 1997, expanded support for shapes with over 255 styles via DefineShape2, added lossless bitmaps (DefineBitsLossless) and 2/PNG/GIF formats, and introduced color transforms and sound effects for buttons, along with debugging via the EnableDebugger tag. Versions 3 through 5, spanning 1998 to 2000, built on these foundations by adding hierarchical display lists, alpha channel support for shapes (DefineShape3) and bitmaps (DefineBitsJPEG3, DefineBitsLossless2), shape morphing (DefineMorphShape), and sprites (DefineSprite) in version 3; dynamic text (DefineEditText) and audio in version 4; and an enhanced ActionScript model with object-oriented features, functions, and asset in version 5, while increasing the maximum tag ID count to 48. From versions 6 to 8 (2002–2005), key advancements included ZLIB compression (CWS files), encoding, device fonts (DefineFontInfo2), Sorenson H.263 video, and Nellymoser audio in version 6, with extended tag lengths for larger records; 2.0 support, script limits, and screen video in version 7; and filters (e.g., blur, ), , bitmap caching (PlaceObject3), advanced gradients, and VP6 video with alpha in version 8, raising tag IDs beyond 48. Version 9 (2006) marked a major shift with ActionScript 3.0 and the AVM2 virtual machine (DoABC tag), EncodedU32 integers, XML metadata support via FileAttributes, and font naming (DefineFontName), requiring players to ignore legacy DoAction tags if the AS3 flag is set. Versions 10 to 14 (2008–2013) introduced flags (UseDirectBlit, UseGPU), deblocking for JPEGs (DefineBitsJPEG4), Compact Font Format (CFF) fonts (DefineFont4), and audio at 16 kHz in version 10; LZMA compression (ZWS files) in version 13; and GPU-accelerated via Stage3D APIs in later iterations, supporting up to 82+ tag IDs and extended length fields from version 6 onward. Subsequent versions from 19 onward (starting around 2013) maintained while adding efficiency improvements like enhanced compression options and support for advanced rendering; version 32, reached in 2020, represents the theoretical maximum for the format's legacy ecosystem, ensuring compatibility with all prior features through header version checks. Throughout its evolution, SWF ensured interoperability by having players ignore unknown tags and scripts specify the Virtual Machine (AVM) version, with file lengths encoded as 32-bit unsigned integers supporting up to 4 GB.

Adoption and Impact

Peak Usage

During the 2000s, particularly from 2000 to 2010, the SWF format achieved its zenith as the dominant technology for delivering rich internet content, powering over 95% of interactive multimedia on the web through . This era saw SWF files embedded via browser plugins become essential for animations, games, and video playback, enabling dynamic experiences that static could not match. Key platforms like relied on SWF for video streaming before the widespread adoption of , with Flash handling the majority of online video traffic—over 90% by 2009. Similarly, sites such as hosted thousands of user-generated SWF-based games and animations, fostering a vibrant community of casual gaming that attracted millions of users monthly. Statistical metrics underscore this peak: by 2005, Flash Player had reached 98% penetration on internet-connected PCs, expanding to nearly 98% of all internet-enabled desktops by and surpassing 1 billion Flash-enabled devices globally by 2010. Corporate adoption was equally robust, with approximately 70% of Fortune 100 company websites incorporating SWF for advertisements and animations during this period. These figures highlight SWF's role in transforming the web from text-heavy pages to interactive environments, used extensively in corporate microsites for engaging user interfaces. Notable implementations exemplified SWF's versatility in interactive media. In 2001, pioneered branded content with interactive banners and microsites using Flash for promotional films like "The Hire" series, blending video and user interaction to captivate audiences. Casual games thrived on SWF, as seen in titles like those on , which peaked at 75 million monthly users, and elements of social games such as , which leveraged Flash for farming simulations on starting in 2009. Video playback via FLV containers embedded in SWF files further solidified its media dominance, enabling seamless streaming on platforms like early . The SWF ecosystem extended beyond browsers through integration with HTML plugins and the introduction of in 2008, allowing SWF-based applications to run as desktop software. AIR enabled cross-platform desktop apps, such as the Pandora One music player, which used SWF components for offline access and rich interfaces, exemplifying how the format bridged web and native experiences during its peak. This integration amplified SWF's reach, with many applications originating in the late .

Decline and Alternatives

The decline of SWF began in the early , driven primarily by persistent vulnerabilities that exposed users to exploits through malicious SWF files. Between 2010 and 2015, faced numerous critical flaws, with reports indicating over 50 (CVEs) annually by 2013, enabling attackers to gain control of systems via drive-by downloads and zero-day attacks. These issues eroded trust, as issued frequent patches that often failed to keep pace with emerging threats, contributing to Flash's reputation as a "giant hole." Compounding security concerns, SWF's lack of native mobile support accelerated its fall, particularly following Apple's 2010 decision to ban Flash from devices. In his open letter "," highlighted Flash's incompatibility with multitouch interfaces, excessive battery drain, and poor performance on touch devices, arguing it hindered the experience. This exclusion from the and ecosystems, which rapidly dominated the market, forced developers to seek alternatives, as SWF content failed to render smoothly on touchscreens without custom hacks that exacerbated latency and resource demands. The market shifted toward open web standards, with HTML5's and APIs emerging around 2011 to handle and interactive animations previously reliant on SWF. Browsers began natively supporting H.264 video encoding, eliminating the need for Flash plugins for streaming, as major platforms like transitioned to video playback. JavaScript frameworks facilitated this migration; for instance, CreateJS provided tools to port ActionScript 3 code to , enabling developers to recreate SWF-based interactions using modular libraries like EaselJS for rendering and TweenJS for animations. To aid the transition, tools like Adobe Scout offered profiling for optimizing SWF performance by identifying bottlenecks in code, graphics, and CPU usage on legacy content. Google's Swiffy, launched in and active until , converted SWF files to and via a cloud-based service, supporting up to ActionScript 3 for animations and simple games, though it had limitations with advanced features. By 2025, SWF sees minimal active development, persisting mainly in legacy e-learning systems compliant with SCORM standards, where emulators preserve archival content; web usage has dropped to less than 1% of sites, reflecting near-total replacement by modern formats.

Standards and Licensing

Published Specifications

Adobe published the SWF File Format Specification as part of its Open Screen Project initiative starting in , with documents covering versions 10 through 19 released between and 2013. These official specifications, distributed as free PDF files, range from approximately 200 to 240 pages each and serve as technical references for developers creating or parsing SWF files. The most recent, Version 19 from 2012, details the binary format's core components, including the header structure, tag-based organization, and support for elements like , audio, and video. Although the official specifications ended with version 19, the SWF format evolved to version 32 to match the final Flash Player 32 release in 2019, with undocumented changes. The scope of these specifications is comprehensive in defining the tag system, which forms the backbone of SWF content, along with associated data structures and the Virtual Machine 2 (AVM2) bytecode introduced in version 9. Tags are categorized into definition types (e.g., for shapes, bitmaps, and fonts) and control types (e.g., for display list management and frame advancement), with precise field layouts and encoding rules. For instance, the DefineBitsLossless tag (type 20) specifies lossless bitmap handling, including support for PNG-compressed data via ZLIB, with fields for character ID, format (e.g., 8-bit indexed or 24-bit RGB), dimensions, and compressed pixel data. A outlines parsing rules using bit-level like unsigned bits (UB) and encoded integers, enabling reliable file interpretation without ambiguity. However, proprietary aspects such as full H.264 codec implementations are omitted, with references directed to external standards like H.264. Prior to Adobe's full publications, released partial SWF specifications from 1998 to 2005, beginning with version 3 in October 1998 and extending to more detailed versions like 7 in 2004. These earlier documents, also available as PDFs, covered basic file headers, initial tag sets, and compression options but lacked the depth of later releases, particularly regarding AVM2 and advanced integration. Following Adobe's discontinuation of Flash Player support on , 2020, the specifications remain freely downloadable from third-party archives and mirrors, preserving access for legacy analysis and tool development. Notable gaps include the absence of Flash Player source code and a deliberate focus on format compliance for third-party SWF writers and readers, rather than runtime implementation specifics.

Licensing Terms and Implementations

The SWF format is a proprietary technology owned by Systems Incorporated, with the Adobe Flash Player runtime distributed free of charge to end-users for playback purposes. Authoring tools, such as Professional (later ), required paid licenses for creating SWF content until the product's official end-of-life on December 31, 2020. Following discontinuation, no royalties are imposed on SWF usage or implementation, and the format is open to reverse-engineering under principles for legacy preservation, though recommends migrating content to modern open standards due to unresolved security vulnerabilities. Under 's stewardship in the 1990s, the permitted free distribution of the Flash plugin to facilitate widespread adoption. Adobe's acquisition of Macromedia in 2005 preserved this model initially, but in May 2008, Adobe's Open Screen Project removed all prior licensing restrictions on the SWF specifications, enabling third-party developers to create compatible runtimes and tools without fees, subject to attribution of Adobe's contributions and adherence to general terms of use. This policy shift facilitated broader ecosystem development while maintaining Adobe's rights over the core format. Key implementations of SWF playback and generation include Adobe's own Flash Player, a proprietary runtime that supported versions up to SWF 32 until its global blocking in browsers starting January 12, 2021. Open-source alternatives emerged to fill the gap, such as Gnash, a GNU Project initiative written in C++ that aims for complete SWF v7 compatibility and partial support for later versions as a standalone player or browser plugin. Lightspark, launched in 2010 and also implemented in C++, focuses on hardware-accelerated rendering for Linux and Windows environments. Ruffle, developed since 2020 in Rust, provides a secure, WebAssembly-based emulator optimized for modern web browsers, emphasizing ActionScript 3 compatibility for interactive legacy content. For server-side authoring, the Ming library offers bindings for languages like PHP, C++, and Python to generate SWF files dynamically without requiring Adobe tools. By 2025, SWF implementations are sustained primarily through Ruffle, which continues active development with nightly releases as of November 2025, under an , while Gnash and Lightspark have limited recent activity, under licenses like GPL and LGPL, primarily for archival and nostalgic purposes, with developers issuing routine security advisories given the format's historical exploit risks.

Flash Ecosystem Formats

The Flash ecosystem includes several proprietary formats developed by Adobe to support the creation, editing, and runtime execution of SWF content, forming an integrated workflow centered around the SWF as the primary runtime format. Source formats for SWF production primarily consist of editable project files. The FLA (Flash Authoring) format serves as the native project file for (formerly ), storing , timelines, scripts, and media assets in a structured . Earlier versions of FLA, prior to Flash CS5, utilized a binary format based on the , which encapsulated all project elements for editing and compilation into SWF. Starting with Flash CS5, FLA adopted an XML-based structure packaged within a ZIP archive, enabling better interoperability and by representing elements like libraries and documents as discrete XML files. The FLP (Flash Project) format, introduced in Flash Professional CS3, functions as a lightweight file that references multiple FLA files and assets, facilitating collaborative development and organization without embedding all content directly. Companion formats enhance SWF functionality by providing reusable assets, data , and multimedia integration. The SWC (Shockwave Component) format packages compiled movie clips, 3.0 classes, and associated assets into a ZIP archive, including a catalog.xml file for metadata, allowing developers to import modular components directly into FLA projects for reuse across SWF applications. The AMF () is a binary protocol embedded within SWF files for remote data exchange, supporting AMF 0 (a simple type-based encoding for objects) and AMF 3 (an optimized variant with compact integer encoding and dynamic class definitions), primarily used in remoting scenarios like Flex applications communicating with servers. The FLV () format acts as a for video and audio streams playable within SWF via the Video class, featuring a header followed by tagged audio, video, and metadata packets, with support for codecs like Sorenson Spark or On2 VP6 for video and for audio. Extensions and variants further support development and automation within the ecosystem. source files use the AS extension and are plain-text files containing code that compiles into SWF , enabling programmatic control of animations and interactions. JSFL (JavaScript Flash) files are JavaScript scripts with the JSFL extension, designed to automate tasks in the Animate IDE, such as FLA files or generating assets. The XFL format represents an uncompressed variant of FLA, introduced in Flash CS5 as a folder-based structure of XML and binary files, ideal for systems like by avoiding binary diffs in compressed archives. These formats interrelate to streamline SWF development: FLA projects compile directly to SWF via the Animate publish process, incorporating AS scripts and optionally embedding SWC libraries for modular and assets; FLV videos integrate into SWF timelines for playback; AMF handles within SWF for dynamic content; and tools like JSFL and XFL/FLP enhance authoring efficiency and collaboration.

Modern Successors

Following Adobe's announcement of Flash Player's end of life in 2020, web technologies based on open standards emerged as direct successors to SWF, enabling rich multimedia experiences natively in browsers without proprietary plugins. For graphics and animation, HTML5 Canvas provides a bitmap-based for 2D drawing and dynamic rendering, allowing developers to create animations and interactive visuals directly in . offers with XML-based definitions, supporting animations through SMIL and CSS, which replicate SWF's vector capabilities while ensuring resolution independence across devices. delivers hardware-accelerated 3D graphics via a based on , enabling complex scenes and effects previously reliant on SWF's Stage3D. Libraries such as PixiJS, which leverages and Canvas for fast 2D rendering, and , a wrapper for and animation, further mimic SWF's authoring workflow for games and interactive content. Interactivity and scripting in modern web development rely on JavaScript (ES6 and later), which powers event handling, DOM manipulation, and logic execution natively in browsers. Frameworks like React facilitate declarative UI construction for responsive applications, while Phaser enables browser-based game development with physics and asset management, often positioned as a Flash alternative for 2D titles. For compute-intensive tasks, compiles high-level languages to a binary format for near-native performance, handling simulations and processing that SWF offloaded to its . Video and audio playback shifted to the native HTML5 <video> element, which supports codecs like H.264 and WebM for streaming and progressive download without external dependencies, eliminating the need for SWF's FLV container and plugin. Migration from SWF involved tools like Adobe Animate, which imports legacy .fla files and exports to HTML5 Canvas documents using CreateJS for JavaScript-based output, preserving tweens, symbols, and interactivity where possible. These open formats enhance cross-platform compatibility on desktops and mobiles, mitigating SWF's plugin-related security vulnerabilities and lack of native mobile support.

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