Flash CS4 ActionScript 3.0 Tutorial
How to Assign Width Property to Button Symbols, Movie Symbols and Text with Flash ActionScript
The width property controls an object's overall width. The values are set in pixels. The object's width alters based on its registration point. For more information about setting and moving the registration point, see topic, Setting and Moving Object Registration Point.
Movie Symbol with instance name widthMovie_mc
Add a Movie Symbol to the stage and click the symbol with the Selection tool.
Open the Properties panel (Cmd/F3 (PC-Ctrl/F3)) and type in the name widthMovie_mc for the Instance Name.
Add a new layer called Actions.
Option double-click (PC - Alt double-click) the keyframe in the Actions layer to open the ActionScript panel.
Copy/Paste the following code to the ActionScript panel.
widthMovie_mc.width = 100;
Test your movie by pressing Cmd/Return (PC - Ctrl/Enter). By setting width equal to 100, the object's width becomes 100 pixels.