I use ffmpeg command line tool. It takes less than 5 minutes to convert audio to mp3. I installed it in my mac using macports. It is simple and it is free.
I've been using Avidemux to convert files for the playbook for some time now with no problems. now i'm running into video files giving me a H.264 message and the file won't convert as normal and wont play on my playbook. any ideas?