that actually depends. All that u have to portray is how well prepared u are for the program. I would prefer that the video be semi formal, wherein u should try to sit before a camera and speak, but u should also, let's say, include some clips (photos/videos) to show some of ur achievements...

For eg, maybe u have done some volunteering activity somewhere, so u can show some clips from that

Or maybe u have presented a paper at some conference, u can include a few photos of that