If you see the following screen when trying to load a video into the Vstrator tool, you need to install Microsoft Silverlight. To do so, click the image in the middle of your screen.
Next, open the Downloads folder on your computer and open the Silverlight.dmg file. Click install to install Silverlight on your computer.
Once you have answered all the questions when prompted, click Close to finalize the installation process on your computer.
Note: You must restart your browser for the install to take effect. If this doesn't work, restart your computer.