If you are making commercial iOS apps, you’ll want a video demo. Video demos can be added to the app store and are great to use in multi-platform marketing and promotions. Keep in mind, a demo is typically short, definitely less than 1 minute and should highlight the core benefits of your app.
For some apps, you can just record the iPhone or iPad screen with another camera especially if you feel you need to show an actual finger doing the tapping. In most cases, however, that’s not necessary and a actual screenshot video would be more effective.