How to add sound / audio file to a video in Ubuntu?

Instructions how to add sound to a video, how to change the sound of a video file in Ubuntu.

Step 1: 
Install Avidemux

Got to the "Ubuntu Software Center", search for "Avidemux" and install it. sudo apt-get install avidemux

Step 2: 
Run Avidemux and open the video file

Start Avidemux avidemux Open the video file.

Step 3: 
Add sound / audio file to the video

Select Audio > Main Track Select Audio Source: "External MP3" "Browse" for the desired "External File" and confirm with "OK"

Step 4: 
Save the video file

While saving the coding will be done, i.e. the sound of the selected audio file will be added to the video.