If you are new to Ubuntu, you would likely try Ubuntu using the Live mode via USB or a virtual machine. These are the easiest way to try the feature of Ubuntu. But, you may notice that by default, Ubuntu cannot play online video using Firefox. Due to legal license issue, Ubuntu does not shipped with non-free codecs. But don’t worry, with a little efforts we can make Ubuntu play online videos for you.
There is an easy fix for this. If you just want to play the online videos, you can copy and paste this command on Terminal.
sudo apt install libavcodec-extra
After install, restart Mozilla Firefox and you should be able to watch your video without problems. Or, for more complete codecs, you can use the following command
sudo apt install ubuntu-restricted-extras
The second command will download more packages. But this will enable you to play MP3 audio format as well as MP4 and some other multimedia formats.
Please note that you have to enable the Multiverse and Universe repository on Ubuntu. To do this, simply open the Software & Update. And then check these two repositories as shown below.