After having updated from Ubuntu TLS 16.2 to Ubuntu 18.4.1 I experienced some problems by reading videos stored on my hard disk, the formats of which are mpeg or mp4. Effects are intermittent stuckings. I thought it could be a good idea to install additional codecs but it has been ineffective and I remember suddendly that I could try tu use the appli VLC instead of the standard Ubuntu appli. "videos": and VLC works well. Now I ask myself if it is usefull tu deinstall the additional codecs I have useless installed.