16/9 on imovie 10.3.3

Unlike the earlier version iMovie 9, iMovie 10 has a 16:9 screen dimension that is the default size and cannot be changed. If you are trying to edit vertical videos, such as from your iPhone, or videos that have an aspect ratio such as 4:3, then iMovie will insert black bars on the side of the clip and/or above it so that it will fit the 16:9 screen dimension. Clips that are larger than the 16:9 screen dimension will be cropped by iMovie to fit the 16:9 screen.

For vertical videos, you can use the Crop to Fill crop setting to make it fit the horizontal screen. However, that would involve fairly radical cropping. Or you can use the Ken Burns crop setting to pan the vertical slip in full screen, and thus be able to view the entire area of the clip. This would work better with photos rather than videos.

-- Rich

O.K. Could you post a screen shot of what you are seeing?

It looks like you might need to delete/reset preferences. To delete/reset preferences, close and then open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects. Possibly you may need to reboot to set the changes. Deleting preferences is a safe procedure that will not cause data loss or disruption to your projects.

-- Rich

Also, you could try simply opening and closing iMovie and see if that solves it. See this thread:

iMovie not filling screen - Apple Community

-- Rich

Well, it still is possible to get an exported vertical video without the black bars. First of all, you can edit a vertical clip in iMovie -- it will just have the black bars on each side that will carry over when exported as well. But, as you will see below, that doesn't make any difference.

There are three ways that you can get an export of a vertical video without the black bars.

1. The easiest way is to create a normal iMovie project, import your vertical clip, edit the clip, and then use the crop tool (the one that looks like intersecting angles) to rotate the clip sideways so that it now fills the horizontal screen in a sideways position. Export it out to your desktop. Open it in QuickTimePlayer and do and Edit/Rotate Clip so that now the clip is right side up with no black bars.
2. Method No. 2 is to go to the Projects view screen (where your projects are displayed as icons) and then do a File/New App Preview. A screen will open that looks just like a regular iMovie project, except that there are limited title choices and other options. However, import your vertical clip into the New App Preview project. It will show as a vertical clip with the black bars. Edit it, and then use the share button (the square with the upward pointing arrow at the upper right hand corner of your screen) to share it to your desk top using the App Preview share option. The project will share to your desktop as a vertical video without black bars.
3. Method number 3 is to edit and share your vertical video from a normal iMovie project to your desktop. The shared movie will have the black bars. However, you can remove the black bars by opening it in QuickTimePlayer, do a Command-Shift-5, and use the controls that appear at the bottom of your screen to drag-select only the video portion without the black bars. Then start the movie playing and record it as it is playing. The resulting screen recording video that is deposited on your desktop will display your vertical video without the black bars.

-- Rich