Race Render and Track Addict. It's a really neat system. If you Google Race Render, you'll find their page and learn all about it.  

The simple version, is you use an OBDII device to log data, a smart phone and a camera to coordinate it all. Then, you bring the video and data file to your PC and setup your custom data overlay.   You'd be surprised how cheaply it can all be done. If you've already got a smart phone, you're looking at under $100.