Once the video uploads, you’ll be able to choose a frame for the thumbnail or preferably upload your own custom thumbnail.While your video is uploading you can set its metadata.Step 3 – Edit Your YouTube Video’s Metadata Click Next to start uploading your file.Click Select File and find the file you just exported from iMovie.Click next and choose where you want to save your file.Under Compress, change the option to Better Quality.The best option is to choose Custom and drag the slider all the way to the right (66 Mbps in our example). However, if your source material wasn’t shot with something with a high bitrate, exporting to ProRes won’t magically make your footage better. The absolute highest quality video codec will be ProRes. Now we have additional options for Quality.The options you see will depend on your project’s resolution. In Resolution choose the highest quality – usually HD 1080p or 4K.In the pop-up window, you can enter a title, description, and tags.Click on Export File (if you want to export just a still for creating a thumbnail, choose Save Current Frame).

Click on the Share button in the top right or go to File – Share.Options for Export File sharing from iMovie Highest Quality iMovie Settings

How to export mp4 in imovie