iMovie exports the final video at the correct resolution based on the device from which your clips were captured
How iMovie knows type of device?
I recorded video using iOS 11 and iMovie is trying to export it with 1920x1080 resolution while original video was 1920x1440.
Why?
As iOS 11 is now public, user-centric queries/comments such as this are perhaps best put to Apple's public community support forums, run by AppleCare, and/or Apple's twitter support account, vs. risking off-topic here in the DevForums, thanks and good luck.
Users can feedback via http://www.apple.com/feedback/ - Individuals using betas are free to use the Feedback Assistant; devs can use the 'Report Bugs' link, below right.
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Tags: off-topic thread
