MKVToolNix and MKVToolNix-GUI is a simple and easy to use application to add or integrate subtitle to a MKV video file. On some video player, like my SONY BluRay Home Theatre the MKV file must be integrate with a subtitle. MKVToolNik is the tool you need to join the video and subtitle.
This tutorial is going to show you how to install MKVToolNix on Elementary OS Luna. Its pretty simple to install this application on Elementary OS Luna.
First, we need to edit the file /etc/apt/sources.list
sudo nano /etc/apt/sources.list
Add the following lines to it
deb http://www.bunkus.org/ubuntu/precise/ ./
deb-src http://www.bunkus.org/ubuntu/precise/ ./
Next, update the system
sudo apt-get update
sudo apt-get install mkvtoolnix mkvtoolnix-gui