Join Date:Joined: Jan 2014
if I was you, first I would look into software, like clearing cache, maybe even full reset, if nothing, then I would open the phone and disconnect the cam and clean connector then plug it back. if that still didn't work and I needed front camera I would look to buy new front cam module and replace it, shouldn't cost more than $20 and there are plenty youtube how to videos.
Of course first and most obvious option would be to send it to Samsung under warranty, but just in case that won't work, you do have DIY options.
Also I'm assuming you're not running custom software or tried to update camera firmware with S5 version for example, because that would be obvious and you would mention it at the beginning.