While InVideo will allow you to easily resize a video on your desktop, you can use InVideo’ s Filmr app to conveniently resize videos for any platform on your iPhone.
Here’s how:
Step 1: Download and sign in to your Filmr account.
Step 2: Click on Camera Roll to upload a video from your gallery or on Camera to shoot a new video.
Step 3: Click on the Format option in the bar at the top of the screen.
Step 4: Select the aspect ratio you want.
Step 5: Click on the arrow icon at the top right corner of your screen to export your video.
And that’s it- your video would be resized to the required new aspect ratio.