Why Flash runs smoother without a wrapper (HTML)

Does anyone know this?

If I load a swf in FlashPlayer standalone, it will play nice and smooth. If I load the HTML it’s embedded in (with SWFObject) in a browser it stutters like hell. If I use my browser to open the swf on its own, that runs nearly as smooth as in the standalone player.

That the standalone player runs smoother is understandable, since it then doesn’t need to go through the browser layer. A slight performance decrease when adding the HTML DOM layer is also understandable, but in my case the difference is huge!

If I were to guess:
Standalone: 100% (benchmark)
SWF in browser: 90%
SWF in HTML in browser: 30%