Audacity is an open source, freeware application with a useful number of features. Click the Audacity icon to download and install it on your Mac.

To be able to change file formats with Audacity, the LAME  library has to be downloaded and installed.

LAME - LAME Ain't an Mp3 Encoder.

Read about it  HERE

LAME installs with no problems on a PPC running OSX. In Leopard on an Intel Mac its not so obvious.

I searched a few forums to get an answer and ended up having to figure it out  with my own few remaining brain cells.

I have included instructions below, on a white background, so that you can copy and paste them to your favorite Text Editor.

Installing Lame for Audacity.

Go to  - http://spaghetticode.org/lame/

Download - libmp3lame-osx-universal-3.97.zip

Go to...  libmp3lame-osx-universal-3.97/package/usr/local/lib/

.... to get - libmp3lame.dylib.

Drag this into....

Audacity 1.3.6 Folder/Plug-ins

At the top of this page you can see the Audacity window with a song file loaded.

Once you have downloaded the Audacity folder to your Mac, drag it into your Applications folder.

Download and install the Lame file.

Double click the Audacity.app icon to launch it.

On the next page we’re going to look at loading a file, cutting it down to form a clip and adding Fade In and Fade Out.

HTML5 audio players have the ability to utilize MP4 files as do some of the more modern flash players like the JWLongtail.

MP4 files have a consider advantage in quality over an MP3 with only a small increase in file size.

Although Audacity doesn’t export files a MP4 (.mp4) per se, it can export M4A (.m4a) which can the be renamed as .p4 if required. It can also export the OGG (.ogg) format required for HTML5 players to work in Firefox.