[CQ-Contest] Audio conversion programs wav -> mp3 ?

[Aurelio - PC5A]

Hello,

Perhaps a bit off topic but I'm looking for a program that:
- will convert .wav audio files to .mp3
- will convert all audio files in a certain directory (batch convert)
- is freeware

I want to use this program to convert all the audio clippings of the 
past contests recorded at Pi4TUE.
Some clippings are now available as .wav at:
ftp://131.155.192.179/audio_files/

After the final submission date of ARRLDX CW I will upload all 3200+ 
clippings.

73
-- Aurelio, PC5A