It seems that there is some confusion about audio conversion tools and some people even pay for them.
The truth is that most encoders, even ones you pay for, use ffmpeg internally to do all of the actual work and ffmpeg is free and open source.
You can even get it pre-compiled for Windows, though the version isn’t great.
The only problem with using ffmpeg directly is that it has a command line interface and most novices find it hard to use.
Here’s a batch file for use on Windows which will convert anything you drop onto the file into a 320kbps mp3:
ffmpeg -i %1 -ab 320k -y %1.mp3 @if errorlevel 1 @pause
To create this file, open notepad. Copy and paste the above 2 lines in. Save it as “convert.bat” or something similar (the .bat is important) and select “All files” from the drop down list.
Put the bat file in the same directory as ffmpeg.exe and simply drag anything you want converted on top of the bat file.
You can use almost anything. wav, m4a, m4v, mov, mpg, avi, etc. If you use a file with both audio and video, such as a movie, it will just extract the audio and save that as an mp3 file.