29.2. Timelines and Frames

Structurally, a .fla file is a hierarchy of one or more animations, each with its own timeline. A timeline is a linear sequence of frames, akin to a physical filmstrip. Each frame can contain audio, video, text, vector graphics, bitmap graphics, and programmatic content.

When a .swf file is exported from a .fla file, the Flash compiler converts the .fla file's timelines to Flash file format (SWF), suitable for playback in a Flash client runtime. When the .swf file plays, the frames from the .fla file's timelines are displayed in rapid succession, producing the illusion of animation. The speed at which the Flash runtime displays frames is governed by the frame rate, which is measured in number of frames per second. (For more information on the frame rate, see Chapter 23).