Media Type - If you enter a filename, the media type will default to the file's extension. You can change it if you wish.

Otherwise, enter the media type for the movie you are adding. If you wish to add more than one media type for the movie, you can add multiple media types on the Edit screen.

If the media type you want is not in the list, you can add it to the Media Types list from the Tools->Options->Miscellaneous screen