ffmpeg: command not found

I successfully figured it out by my self, here is how.

1. remove the current ffmpeg by running:

   sudo apt-get remove --purge ffmpeg
   

2. Add ppa trusty-media for 14.04:

   sudo apt-add-repository ppa:mc3man/trusty-media
   

   For 16.04, add the following Repo:

   sudo apt-add-repository ppa:jonathonf/ffmpeg-3
   

3. Update repo:

   sudo apt-get update
   

4. Finally install it:

   sudo apt-get install ffmpeg