Saving a movie in a Seagate Expansion and not the hard drive

Your program files must be on your computer's C drive. You can certainly output your finished movie to any drive you want. Even an external drive.

It's also possible to have your project files and media files on a second or even external drive, which can save you space on your C drive. But working on an external drive can mean diminished performance, depending on how powerful your computer is and how you fast your connection is.