Since you state you want to "hook up a microphone", then I'll assume you're talking laptop, tablet, or desktop PC.
If you've already got a whiteboard app, and just need the "recording" feature, there are a number of applications that record video and audio on your system. Some of them are desktop applications. To find them search for "Capture Video Audio" in the Windows Store.
I really don't know of a whiteboard app that records video and audio to be honest. Not that they don't exist, but that I haven't had need for one and haven't done a thorough search, and my current time constraints won't allow it. Sorry.