For xUbuntu 12.04 run the following:
Keep in mind that the owner of the key may distribute updates, packages and repositories that your system will trust (more information).
echo 'deb http://download.opensuse.org/repositories/devel:/OBS:/Light:/Stable/xUbuntu_12.04/ /' | sudo tee /etc/apt/sources.list.d/devel:OBS:Light:Stable.list
curl -fsSL https://download.opensuse.org/repositories/devel:OBS:Light:Stable/xUbuntu_12.04/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/devel_OBS_Light_Stable.gpg > /dev/null
sudo apt update
sudo apt install obslight-fakeobs