Today I deleted my Win partition and started using Ubuntu as my main and only OS. I am using Ubuntu 14.04.02 LTS updated, fresh installed yesterday.
The thing that bugs me is this:
As I can play mp3, view youtube etc. even now without Ubuntu restricted extras; if I do not install them, what will my Ubuntu experience be like?
To see this a bit more through:
sudo apt-get install ubuntu-restricted-extras
You'll get all that needed to play any content of media, though the most important ones.
The items that you will install include the following (and you can also install them manually with apt-get install e.g.:
Flashplugin-installer
gstreamer-ffmpeg
gstreamer-pitfdll
(helps with Windows binary codec play)
gstreamer-plugins-bad
gstreamer-plugins-bad-multiverse
gstreamer-plugins-ugly
gstreamer-plugins-ugly-multiverse
icedtea6-plugin
(java browser plugin for java applets or other even your choice I use everything from Oracle Java for example)
libavcodec-extra-54
(linux ffmpeg codec – used in majority of files, if you are interested in streaming or transcoding, you should additionnally install libavcodec-extra-54)
libmp4v2-2
ttf-mscorefonts-installer (Microsoft fonts for better display)
Also I installed manually:
sudo apt-get install lame flac
But I just needed those because of doing some encodings/decodings they give a bit more advanced options when ripping or converting audios e.g.
And one more alternative is VLC media player it has its own set of codecs and you can basically play what you desire.
You can install it with:
sudo apt-get install vlc browser-plugin-vlc
or with this official ppa:
sudo add-apt-repository ppa:videolan/stable-daily
sudo apt-get update && sudo apt-get upgrade
sudo apt-get install vlc
As one of the comments stated above you do not need it if you only plan on using free codecs.
HOWEVER, you are going to find your computing experience limited. You will not be able to watch movies(DVDS), use any site the need a Flash player, listen to MP3's. (I know you question states that you and do some of these things but, you will likely find some that you cannot in the future. Some purchased MP3 will not play without them)
IF you use Google's Chrome (not chromium) it will include flash in the browser but no other browsers will.
Short answer here is: you do need to install them, but if you want all the functionality that you have become accustomed to in Windows you will want to install them.
