I am trying to download new stuff for Kdenlive, but I keep getting the "Loading of providers from file https://kdenlive.org/data/rendersources.xml failed".
When I go to the link it says it's loading content from, I get an error message saying that the site doesn't exist.
"Download new wipes" is the only one that works, so what is going on here?
Oh, and I'm using the latest version from the Sunab PPA (4.15.12).

Sunab PPA's are completely out of date: release held at 15.12, master at 16.07: we now are at 17.04 and 17.07 respectively.
You should rather use ppa:kdenlive/kdenlive-stable
I believe GHNS has been restored since then (just a server address change or so)

See. The problem with your PPA is that it can't verify the GPG key. Couldn't for me at least. And its packages conflicts with Trusty when I try to upgrade MELT.
The PPA I use included the necessary packages for that and I wouldn't say it's that dated. Only a few versions behind (15.12.1).
Your PPA wouldn't allow me to update MELT without breaking packages, so I had to purge that one.
Btw, you guys should really create a Trusty build for your newer versions of Kdenlive as Trusty and Mint 17 are LTS versions and good for another 2 years.
Either do that or include the packages necessary to upgrade MELT and Kdenlive without breaking Ubuntu Trusty or Mint 17 and 18.


EDIT!
I am now on the latest version of Kdenlive after some tinkering around, editing packages, downloading packages manually from the Ubuntu site and stuff.
It works great. Not a very user-friendly way of doing it. So again, updating the PPA for Ubuntu 14.04 and Mint 17 people would have been nice.

Normally "sudo add-apt-repository ppa:user/ppa-name" handles the GPG key import. If it fails there's another problem…

Sorry but trusty (14.04, base for mint 17) is not supported any more (LTS = 2 years support, and only for security bugs)… The current LTS is xenial (16.04).
14.04 even didn't have Qt5, so no chance any Kdenlive version >= 15.04 can work on it!
We can't offer updates to users choosing to keep a prehistoric OS

EDIT: sorry again I was wrong, LTS are released every 2 years, but support is 5 years. But again, no software upgrades, only critical bugfix…

LTS are 5 years now, with a new LTS every 4th year. So Trusty is supported til April 2019 and the next LTS version comes out april 2018.
Besides, a lot of people don't like tinkering, so they keep the LTS version for as long as they can.
But anyway, I got the latest Kdenlive working beautifully on my system now, so that's great.