Use a screen recorder of video capture software. There are several available at a good price. I agree that you should have a demo in place. But, you can save time by doing a simple demo with a screen recorder. If there is true interest in your app you can then move forward.
Don't stop taking massive action.
Best of Luck,
Michael T. Irvin
michaelirvin.net
My books are available exclusively through Amazon Books. Check out my book "Copywriting Blackbook of Secrets"
Copywriting, Startups, Internet Entrepreneur, Online Marketing, Making Money