Exporting Resolution in IMovie

iMovie's screen dimensions are 16:9 (1920 x 1080), and that cannot be changed. Anything larger than that will be cropped, and anything smaller will have black bars around it to make it fit the 16:9 screen. The resolution export options are limited to 540, 720, 1080, and 4K.

Try displaying the clips with the "Fit" setting rather than the "Crop to Fill" setting and see how that looks.

-- Rich

It's a little hard to address the issue without having hands-on with your Mac.

Can you send a screen shot of what you are seeing on the iMovie preview screen?

The resolution and frame rate of a project are set as that of the first video clip inserted into a newly created project. Was your 1680 x 768 clip the first clip added to a newly created project?

-- Rich

You are getting no 1080 option because the clip or project is not a 1080 project. I get the same thing, as you can see from the below screen shot. 1080 is grayed out because the project is not 1080.

When I export a higher resolution clip or project, I do get the 1080 option:

Click on the settings button above and to the right of the timeline. At the top of the display box that appears you will see the resolution setting of the project.

Regarding the screen shot that you posted, the preview screen display that is shown is displaying a 16:9 video exactly as intended by iMovie. No way to change that, unfortunately. I'm not clear why you believe that that is a problem, as 16:9 is an optimum dimension for viewing on a wide screen.

Lastly, iMovie does not change the resolution of a movie. The resolution that you import is the resolution that you get out, unless you manually change it in the export settings.

-- Rich