When I drag a clip to the timeline it changes to 4.3

Hi,

iMovie does not change the aspect ratio from the original aspect ratio of the clip. Assuming that the crop is set to the "Fit" option, a video clip or photo originally shot in 4:3 will import into iMovie as a 4:3 clip, with black bars to make it fit iMovie's 16:9 screen. A video or photo shot in 16:9 aspect ratio will import into iMovie at 16:9.

If you have a 4:3 clip and want to display it in iMovie at 16:9 you would need to select it and click on the crop tool (the one that looks like intersecting angles) in the tool bar at the top right of the screen and choose the "Crop to Fill" option from the crop controls. Or, before creating the project, you can do iMovie/Preferences and set the photo placement at "Crop to Fill" or "Fit" as you prefer. Then clips imported afterwards will conform to the default setting that you have chosen.

If you use Crop to Fill on a 4:3 clip, it will display at 16:9, but part of the clip will be cropped to make that happen.

-- Rich