MP3 is an acronym (or file extension) for "MPEG Audio Layer 3". These are compressed audio files which can be played on a computer using an MP3 player. (MPEG stands for Motion Pictures Expert Group, which is a US standards organization responsible for full motion video standards.) MP3 was developed by the Fraunhofer Institute IIS and is restricted to audio data, in the same way as mp3PRO, which was developed by Coding Technologies.
Nero can compress both MP3 and mp3PRO files, both of which have the file extension MP3. MP3. The quality of the signal depends on the compression rate. The standard rates are 64 kbps at 44100 Hz stereo for mp3PRO and 128 kbps at 44100 Hz stereo for MP3. During the encoding process the original WAV file is generally reduced to about 5 percent of its original size in mp3PRO format and to about 10 percent in MP3 format. The encoding process is lossy, but the psychoacoustic models remove only those parts of the audio file which are considered to be inaudible. Audible parts of an audio file can only be lost at a high compression rate.
Nero allows you to convert 30 files into MP3 or mp3PRO format. For licensing reasons, it is not possible to convert more files. You can find both the plugins which allow unlimited encoding on Ahead Software AG's website: Ahead Webshop.