Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Editing › Editing .mov files › It’s rendering (saving) it as
It’s rendering (saving) it as an mpeg file because that’s what you told it to render as.
Movie Studio has a number of different render options with mp4 being one of them.
If you haven’t already done so, the manual is a great place to start. Sony has a number of tutorials on their site at http://www.sonycreativesoftware.com/training/moviestudio that are well worth your time watching as you learn the software.