No, once you have started your demo, pause it, go in third person (thirdperson in console) and then mirv_input camera. Then, you will be able to move around freely and you will see yourself too. If you do not go thirdperson first, only your hands will be visible.
Once you do mirv_input camera, find yourself a location where you want to record from, then type mirv_campath add in the console. Press escape, go to the end of the action that you want recorded, repeat the same stuff above.
NOTE: You might want to have something to aim at as a reference because you will have to manually go to your desired location each time using WASDXZ so the camera looks static.
After you've added your second camera and pressed escape, you can just unpause the demo, type mirv_campath add twice (doesn't matter where in your demo, input camera isn't necessary) so you have at least 4 points so you the smooth works, and flex it after