Your earnings from video ads will depend on the pricing of the specific video ads you display. Video ads can be either cost-per-click or cost-per-thousand-impressions. When paid on a CPC basis, you'll receive earnings for each valid clickthrough on ad -- that is, a click on the display URL or playing video that directs a user to the advertisers' website. When paid on a CPM basis, you'll be paid for impressions of the opening image, rather than plays of the video.
If you’ve got a fitness app, you might have segmented your potential audience into 2 groups. Men who want to get huge lifting weights, and men who want to get ready for a marathon. As you can imagine, they have completely different goals, and their interests and behaviour will reflect that. You need to take this into consideration when you create your images.