Come now, and let us reason together, saith the LORD: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.
Isaiah 1:18 (NHEB)
Non-open source Audio and Video related software (some involving patents) such as gstreamer, mp3, mp4, unrar and various audio and video codecs may be added via a meta-package called Ubuntu Restricted Extras.
Open a Terminal [Ctrl]+[Alt]+[T] and type:sudo apt install ubuntu-restricted-extras -y
EULA for Microsoft fonts: Hit [Tab] to select <OK>, [Enter] to “press” <OK>
Left arrow to select <Yes> and [Enter] to “press” <Yes>
To watch movies on DVD, you’ll also need the libdvdread4 package
Open a Terminal [Ctrl]+[Alt]+[T] then type:sudo apt install libdvd-pkg -y
In the pop-up dialogue box press [Enter] to select <OK>
Press [Enter] to select <Yes> to enable auto-upgrades.
then type:sudo dpkg-reconfigure libdvd-pkg
In the next dialogue box, hit [Enter] to select <Yes> to download, build, and install libdvdcss2.
Watch DRM-protected HTML5 audio and video in Firefox: go to Menu > Settings, scroll down to Digital Rights Management (DRM) Content and check the Play DRM-controlled content check box.
History (or why this stuff isn’t included already) See Restricted modules in Ubuntu in the Ubuntu Mailing List (2009), Why Watching DVDs on Linux is Illegal in the USA on How-To-Geek (2017) and Driven by necessity, Mozilla to enable HTML5 DRM in Firefox on Ars Technica (2014).