Both App Store and Google Play Store offer the option of uploading an app preview video. It's a great way to show your app's functionality, features, and UI. If you want to convince new users to download your app, there's nothing better than the good old "Show, don't tell" technique.

The recipe for a great video is similar for both platforms:

• Try to keep your video under 30 seconds (App Store doesn't support longer videos. Google Play Store does but only the first 30 seconds autoplay).
• Tell a cohesive story that gives users a sense of the journey they'll experience when using your app.
• Make your point within the first 5-10 seconds.
• Show off the actual app experience and include the most appealing features.
• Consider adding text elements to give the user context if the video is muted, but make sure they are large enough and stay visible long enough to read.
• Provide localized videos for specific regions and languages.

Technical requirements like orientation and aspect ratios, however, differ a little for both platforms. And, of course, the video for each platform must use that platform's UI — seeing Android UI in App Store or vice versa will be confusing. Always check the latest requirements on the respective websites, as they are subject to change.