I'd say the best option to have a smooth outcome is to use the Aspect Ratio Calculator for whatever resolution you'd want to animate http://andrew.hedges.name/experiments/aspect_ratio/
When it's done, simply add a "fullscreen" button on the edge like The-Weebl does
Ladies ladies I know all about making bablies
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and export it with all the .html page assets (you'll only have to open the .html file for the .swf to play) if the computer it'll be viewed on won't have the stand-alone flash player.