The Anytune export feature uses the M4A/AAC file format.
AAC is the successor to mp3, and produces better quality audio at the same bitrate when compared to mp3 encoded songs. AAC is widely supported by hardware manufactures, including Apple. In fact, songs downloaded from iTunes are encoded using AAC.
WikiPedia has a good discussion of the advantages of M4A/AAC.
Sorry to bother you mate, this seems to be the only thread about audio conversion? i have a question here and may i have your answer? I downloaded a AU audio file on the internet (about my own job) but it cannot be played on my VLC player and I do not know why. I download this audio converter as you can see (http://www.videoconverterfactory.com/tips/au-to-mp3.html) to convert this AU file. But before conversion, it required me to preset parameters, i know i should choose MP3 as my out put format. But what is about the bit rate and sample rate, ? What are the meaning of these two parameters and their connections? What should i do, does any one know?