Loading files to play .mp4 video causing dpkg error & blocked Terminal screen

Question

O/S; Ubuntu 19.10 on AMD (Ryzen5).

Objective; To play .mp4 video clips.

Steps taken:

1. Ran:

   sudo apt install libdvdnav4 libdvdread4 gstreamer1.0-plugins-bad gstreamer1.0-plugins-ugly libdvd-pkg
   

   The install seemed to have proceeded without any problems, but the Terminal screen then filled with the following, became totally unresponsive & required a New Tab to progress.

   

2. Attempted to run instruction from screenshot:

   sudo dpkg-reconfigure libdvd pkg
   

   This resulted in an error message saying:

   debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable
   

3. Attempted to run

   sudo apt install ubuntu-restricted-extras
   

   resulting in error message:

   E: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 5777 (dpkg) - open (11: Resource temporarily unavailable)
   N: Be aware that removing the lock file is not a solution and may break your system.
   E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?
   

4. Attempting to uninstall/purge resulted in another error message saying 'dpkg was interrupted, you must manually etc, etc' and to run:

   sudo dpkg --configure -a
   

Running this resulted in the same unresponsive Terminal screen as above Terminal Screen screenshot.

Any advice on how to proceed from here would be most appreciated.