Since your app is content driven you should definitely try to animate the user to get started and start uploaded his first mediafile and/or connect with people.
You could do this with a process that maybe involves a bit of gamification, for example provide something like a percentage status and make uploading a mediafile part of that.
You could also show new ...
I would suggest to show a getting started guide like information. Maybe 5 good to know facts presented as you would later show photos or videos. The user can click on it and gets more information in a popup or the browser opens etc.