Sometimes you might be tempted to 'get special codecs' so you turn on partners, it leaves you vulnerable. Use the inbuilt Firewall and your system will be stable.
While this is not bad advice, development and extra repositories can provide helpful software and solutions. Vlc is accessible by
sudo apt install vlc. You can get the codecs by including the restricted repositories and then typing
sudo apt install ubuntu-restricted-extras on the command-line.
Most repositories are not problematic. Ppa's are maintained rigorously with a strict and precise posting procedure. Our very own Aravisian is a contributor and can remove any doubts you have about possible nefarious software in the repositories. It's much safer than windows app store! Money won't get you anywhere in Linux!
Thanks, Harvey, I was just speaking from experience, I went and turned it on and my screen started glitching crazy. I had to save important 3D home files and then reinstall the OS to clear the issue.