"Moonlight 1.0, which was officially released Wednesday,
automatically downloads a proprietary codec pack from Microsoft in
order to provide Linux users with legally licensed support for
Microsoft's video formats. Bockover's plugin uses the NPAPI to
register itself as the default consumer of Windows Media content
and then, when it is invoked by the browser, uses Moonlight to
embed a Silverlight-based streaming video player—which he
wrote entirely in XAML and JavaScript—in the page to handle
WMV.
"Linux users typically rely on embedded Totem or MPlayer plugins
to view streaming WMV content in the browser. This can be
problematic, because it requires the user to obtain the Microsoft
codecs on their own, by buying them commercially from Fluendo or
using unlicensed codecs obtained from servers outside of the United
States. Moonshine eliminates that complexity and legal ambiguity by
allowing users to watch WMV content with fully licensed codecs that
are obtained directly from Microsoft with an automatic
updater."