Edit: Issue is not specific to Mavericks, but seems to be rooted in the power saver feature of Safari. Mediasite is looking into the problem, a workaround is available from the following link: support.sonicfoundry.com/Knowledge/Article/000003845
When attempting to view a presentation in Safari 7.0 on OS X 10.9 (Mavericks), the video does not play.
This will also impact other portions of Mediasite where Silverlight is used for video playback, such as within the Web Editor application and the Recorder Monitor within Management Portal.
Safari 7.0 includes a new feature called Safari Power Saver, which is intended to disable plug-ins in order to conserve battery power.
When hovering over the video window of a presentation, there should be an icon that appears which you can click on in order to allow the plug-in on that webpage. However, we have seen cases where this icon does not appear properly. If this happens, you must disable Power Saver completely in order to allow the plug-in to run. To disable the Power Saver function, enter Safari Preferences, go to the Advanced tab, and uncheck the box to "Stop plug-ins to save power". Reload the webpage containing the Mediasite presentation and it should play properly.
This issue is pending further investigation by Sonic Foundry.