As the instructor, you can upload videos as:
Students can upload videos as assignment submissions. When students upload a video, they can choose to make it available to the entire class, just a group of students and you, or only you. Students use basically the same procedure as you for uploading their videos. For more information, see the MediaShare Student Help.
When you create or edit an assignment, you can select the option to moderate student submissions. You can then view each submission and decide whether or not to publish it.
What happens when MediaShare uploads a video? | Video size and upload times | Videos in MediaShare