Do you know how this camera/mic functionality is offered on the site? I'm guessing it is likely a Flash, Silverlight, or Java plugin. There's nothing for HTML5/native web that offers that I believe.
And as such, you likely won't be able to deal with it with Selenium alone, especially if the plugin code for that is not yours (e.g. you can't instrument the plugin to allow API scripting against it).
Your last resort workaround is to combine Selenium with tools like Sikuli and/or AutoIt, which could handle manipulating the plugin. But the caveat to that, is integrating such tools, you can't really deploy in a Selenium Grid or parallel testing fashion w/o knowing specifically which node to execute the test on because Sikuli/AutoIt are not "grid" enabled unlike Selenium.