How to compress a video on iPhone
Short answer
Apple's own method uses the free iMovie app: make a movie from the clip, then share it at a lower resolution (720, 540 or 360) and save it. You then have two copies and must delete the original yourself. Converting 4K to 1080p keeps the video sharp on a phone screen and uses a fraction of the space.
Apple's method: iMovie
Apple documents this for iPhone 12 or later with iOS 26 or later and the free iMovie app.
- In iMovie, tap Start New Project › Movie, tap Media › Video, and choose the clip.
- Tap Create Movie, then Done.
- Tap Share › Save or Share Video › Options, and pick a smaller resolution.
- Tap Save Video. The smaller copy is saved to Photos.
- Check the new file's size with the Info button, then delete the original if you're happy with it.
It works, but it's one video at a time, the smaller copy is a new item that isn't in the original's albums and may not keep its date and location, and you have to find and delete the original yourself.
Why 1080p is the sweet spot
Even the largest iPhone screen has well under half the pixels of a 4K frame, so on the phone a 1080p copy is very hard to tell apart. 4K earns its space on a large TV or when you edit. For clips you watch on your phone or share in messages, 1080p is plenty.
Doing it with SlashPhotos
SlashPhotos makes a 1080p copy at 30 fps of any large video, plays you both versions side by side, and only swaps them if you say so. The copy keeps the original's date, location, albums and favorite. A 3-minute 4K60 clip drops from about 1.1 GB to about 200 MB. The original goes to Recently Deleted, so you can still get it back for 30 days.
Questions
Does compressing a video lose quality?
Some detail is lost going from 4K to 1080p, but on a phone screen the difference is very hard to see. Always compare both before deleting the original.
Can I compress a video in the Photos app?
Photos can trim a clip, but it can't lower the resolution, and edits in Photos keep the original so you can revert them. To make a smaller copy you need iMovie or another app.
Will a compressed video still be in iCloud?
With iCloud Photos on, the new copy uploads like any other video, and the original is removed everywhere once it leaves Recently Deleted.