Calibre might not support directly transferring mp4/mp3 files to USB through its user-defined driver plugin. A workaround could be manually copying the files to your USB from the Calibre library folder on your computer. Alternatively, I've been using the Movavi app for nearly a year for video editing, resizing, and more, which might help your situation. For further details on its features, you can check out
https://www.movavi.com/support/how-t...eo-editor.html.