About SWF

Brief History

At the very beginning, a company created the SWF format to generate small vector animations on the Internet called Shockwave Flash (hence the name of the format, SWF.) It also included images. This company was bought by Macromedia around 1997 (if I recall properly). This is when Flash v3 was created. Since then, Macromedia created a new version about once a year up to version 8. At that time (in 2005/2006), Macromedia sealed a deal with Adobe which wanted to use the SWF format in their PDF files.

Today (May 1st, 2008), the SWF format is available for free to all.

There was also a project called Open Screen Project that will help everyone to get access to the Flash craze. That should help and plus Adobe is releasing many information and making more and more things free. That rocks, in a way.

What is SWF?

SWF (pronounced like swiff by some, but really is is S, W, F) is the file format used to describe movies built of mainly two graphical elements: vector based objects and images. The newest versions also accept external modules, sound, video and interaction with the end user using ActionScript.

The file format was first created by a small company that Macromedia purchased early on. The main goal of the format was and still is to create small files of highly entertaining animations. The idea was to have a format which could be reused by a player running on any system and which would work with slower network (such as a browser connected to the Internet with a slow modem.) The format is fairly simple also.

This document presents the SWF format and includes code examples for really difficult points (like bit fields) and it explains with words what is really not clear otherwise. I hope this document will help you in developing your own players and/or generators of SWF file formats.

The geometry in SWF

The SWF file formats uses several types of objects. The ones used the most are called shapes. These are vector based objects which can be rendered really fast in 2D. The other type of graphical objects are images, fonts, colors and matrices. More information about the SWF geometry is given in the Appendix A below.

In different versions of SWF they also added different graphical enhancements. In version 6, they added support (somewhat flaky, fixed in version 7) for internationalization. In version 7 they added much better support for small fonts. In version 8 they added support for transparent videos. You can see the evolution by looking at the different tags and the tag structures (many times, a tag was enhanced in a version without the need to create a new tag.)

Multimedia content in SWF

The SWF file format has evolved to support more and more multimedia formats. It started with 2 audio formats (raw uncompressed and ADPCM) and it now supports many audio and video formats.

Because multimedia files tend to be large, the SWF format was also enhanced to allow you to load separate multimedia files as required. This is done using the FLV files. These files can also include scripts.

Interactivity support in SWF

At the very beginning, SWF was only for animations. You started it, it played a loop forever until you'd move on to another web page.

In version 3, better support for keyboard and mouse clicks was added. This was rough and didn't offer much possibilities beyond a simple switch (i.e. if you click start playing B instead of A). Since version 4, Macromedia added support for a scripting language. This is very similar to what Sun has done with Java. This is an interpreted language running within the Flash player in its own environment.

Real interactivity came with version 4, but real scripting came only in version 5. That is, since version 5 you got real objects. At that time Macromedia decided to be more compliant with what ECMAScript described in their specification. Yet, they used the free Netscape interpreter available (if I'm correct) in Netscape 4. This was pretty bogus. They kept trying to enhance that interpretor until version 7. In version 8, they finally did a full rewrite (i.e. got the new interpreter from FireFox) to really support ECMAScript properly. This means there are some inconsistencies between older versions (DoAction) and version 8 ABC code. Running your older scripts may fail in version 8 when compiled as ABC code. Don't be too surprised!

With version 8, they also very much improved their library coming with their Flash builder product.