| As a movie plays, the timeline's playhead travels from frame to frame. Each time the playhead enters a new frame, the interpreter executes any code attached to that frame. After the code on a frame has been executed, the screen display is updated and sounds are played. Then, the playhead proceeds to the next frame. For example, when we place code directly on frame 1 of a movie, that code executes before the content in frame 1 is displayed. If we place another block of code on a keyframe at frame 5 of the same movie, frames 1 through 4 will be displayed, then the code on frame 5 will be executed, then frame 5 will be displayed. The code executed on frames 1 and 5 is said to be executed synchronously because it happens in a linear, predictable fashion. All code attached to the frames of a movie is executed synchronously. Even if some frames are played out of order due to a gotoAndPlay( ) or gotoAndStop( ) command, the code on each frame is executed in a predictable sequence, synchronized with the movement of the playhead. |
