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

qtgstreamer-declarative is installed in your system.

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

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

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

qtgstreamer-declarative package basic information: