I said this because in the past I've used few audio encoders which are both GUI and command-line ones and even though some had decent GUIs yet they weren't that optimized and as a result they took more time that it should.
In that sense Lame is one of the best MP3 encoding command-line applications that I've come across (I'm pretty sure I ain't alone for that thought). Although by default there isn't an official GUI yet it's extremely fast and easy to use as well. It's actually one of the widely used app by many other applications + there's even a gstreamer plugin which enables it to integrates with Gstreamer.
Anyway, if you want to encode MP3 files fast and okay with using a command-line tool then lets install Lame. I'm assuming that you're using Ubuntu 11.04 Natty Narwhal but this should work on 10.10 and 10.04 versions and in other older ones I think.
Open your Terminal and enter the below command.
sudo apt-get install lame
That it!. But as said this is a command-line tool so I recommend that you read its manual which you can access by entering the below command afterward (or anytime you want to read it).
man lameBut as mentioned before if you have a lot of files to be encoded then lame can be a bit frustrating. If so, then lets install a GUI which uses the Gstreamer-Lame plugin called Sound Converter which is pretty darn easier to use.
If you use Ubuntu 11.04/10.10 or 10.04 you can install Sound Converter by entering the below command in your Terminal.
sudo apt-get install soundconverter
But we also need to have install the "Gstreamer-plugin-Ugly" package, if you have already installed it then you're good to go, if not we have to install that too.
Enter the below command in your Terminal again (this is for Ubuntu 11.04, but depending on your Ubuntu and Gstreamer version, only change the "0.10" number).
sudo apt-get install sudo apt-get install gstreamer0.10-plugins-ugly-multiverseOnce installed you should be able to run in via: "Applications" -> "Sound and Video" -> "Sound Converter"
Or simply press "Alt" + "F2" and enter the below text into the box.
soundconventerThanks to the Gstreamer "ugly plugins" you can not only use sound converter to convert MP3 files but it can also be used to convert Ogg, Flac, Wav as well. Enjoy!.