$ sudo apt-get update
$ sudo apt-get install qtgstreamer-plugins 

qtgstreamer-plugins is installed in your system.

Make ensure the qtgstreamer-plugins package were installed using the commands given below,

$ sudo dpkg-query -l | grep qtgstreamer-plugins *

You will get with qtgstreamer-plugins package name, version, architecture and description in a table

qtgstreamer-plugins package basic information: