1. lock your camera off on a tripod. do not move the camera.

2. ensure you don't change the lighting, camera etc from steps 3-5

3. record yourself playing guitar

4. record yourself playing keyboard

5. record the room without anything happening. this is called a clean plate

6. use the clean plate to remove the background from the guitar and keyboard shots, leaving (hopefully.....) just you playing an instrument. this procedure is called a difference key/difference matte.

7. now you can composite you, on both keyb and guitar, over the top of the clean plate you shot earlier.

use a program like after effects, shake or nuke to perform this procedure.

Dan