Reframe It takes a horizontal video, lets you choose the subject, then automatically crops around them giving you a vertical video perfect for social media content. It will zoom, pan and crop automatically.

Features include:
Change the crop size and orientation instantly without reprocessing.
Automatic person and face tracking.
Tap on a person to change focus.
Manual panning by dragging the crop area while the video plays.
Auto zoom and manual zoom
Rewind and reposition the crop area at any time.

Terms of use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/