If we ignore Flash and Silverlight, the only reasonable things that come to mind are Java applets (please do not do this), custom browser plugins (a lot of work and who wants to install the plugin just use Chatroulette ...) and just use <object> element and rely on any media player that the user may or may not install (this will not give you very good control over anything).
In general, I would not say that it is impossible to do this without using one of the aforementioned, fairly widespread plugins.
Matti Virkkunen
source share