Ubuntu – Unable to locate package libgstreamer0.10-dev on Ubuntu 18.04

I'm trying to install OpenCV4 as explained here: https://www.learnopencv.com/install-opencv-4-on-ubuntu-16-04/

When I get to

sudo apt -y install libgstreamer0.10-dev libgstreamer-plugins-base0.10-dev

I receive

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package libgstreamer0.10-dev
E: Couldn't find any package by glob 'libgstreamer0.10-dev'
E: Couldn't find any package by regex 'libgstreamer0.10-dev'
E: Unable to locate package libgstreamer-plugins-base0.10-dev
E: Couldn't find any package by glob 'libgstreamer-plugins-base0.10-dev'
E: Couldn't find any package by regex 'libgstreamer-plugins-base0.10-dev'

I have checked online and the packages are available at https://packages.ubuntu.com/search?keywords=libgstreamer0.10-dev

I tried manually downloading and installing with

sudo apt install ./libgstreamer0.10-dev_0.10.36-1.5ubuntu1_amd64.deb

Which gives me

Note, selecting 'libgstreamer0.10-dev' instead of './libgstreamer0.10-dev_0.10.36-1.5ubuntu1_amd64.deb'
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libgstreamer0.10-dev : Depends: libgstreamer0.10-0 (= 0.10.36-1.5ubuntu1) but it is not installable
                        Depends: libglib2.0-dev but it is not installable
                        Depends: libxml2-dev but it is not installable
                        Depends: gir1.2-gstreamer-0.10 (= 0.10.36-1.5ubuntu1) but it is not installable
E: Unable to correct problems, you have held broken packages.

I'm new to Ubuntu (only used Manjaro). I don't understand why apt can't locate a package if it's on the website.