I'd like to know how to produce this kind of instructional video, where an actor is writing on an invisible wall facing the camera:
Introduction to Limits (mathbff)
What equipment/tools and which setup is required to shoot this video?
You need a few simple things to do this:
Record your actor writing on the glass. To the camera, the writing will appear backwards. Use your editing software to flip the image horizontally. The writing will now appear normal*. Most editing software is capable of this operation. If there's not a "flip horizontal" command, try setting the horizontal scale to -100%.
*Pro tip: Make sure your actor's clothes don't have any writing on them, or it will appear backwards in the final result.