In overview, VSD can't play media clips by itself, it has nothing to do with that. When you are previewing a page it's using a basic browser. Whatever is used, the browser that calls up your HTML page has to have some sort of plug-in or other device installed to play media, unless you supply one yourself such as the CC Jukebox. What I think is happening is the preview browser, told to play an audio clip, is trying to call up what it has defined as the default player for mp3, which just happens to be ffdshow. The issue you've been happening is outside the scope of VSD, and into the realm of browsers-playing-media.
But if you can navigate to where VSD is exporting the HTML pages, and open them with your test browsers without problem, then the issue is just how VSD is trying to preview them. In either case the issue is the software being called to handle the mp3.
Hopefully that makes some sort of sense.
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