Check the supported video audio formats lists of iMovie and QuickTime and you'll get a whole picture.

And the video audio codecs supported by iMovie and QuickTime are not 100% identical. Not all video and audio codecs in MP4 format are supported by QuickTime. MP4 is a container format - a box that contains your video, audio, and metadata.

The video file exported from iMovie is usually formatted as MP4. Convert iMovie Export File to QuickTime Best Format Upgrade macOS to the latest version if needed. Therefore, check your iMovie export and Mac operating system. Cuz all Macs on High Sierra or higher OS will support HEVC playback with Mac's default QuickTime player. If your iMovie export MP4 footage is formatted by HEVC (x265) codec, your QuickTime player can't smoothly play iMovie MP4 HEVC video unless your QuickTime player is running on macOS High Sierra or higher operating system. Delete the iMovie PreferencesĬheck your iMovie export file first.

Top Solutions to iMovie Export Incompatible with QuickTime Issue

Exporting from imovie