I'm using the MP3 PRO encoder that's made by the fraunhofer institute, those
that have the original MP3 patent, so I'm guessing that they must follow some
MP3 standard :-).
Many free decoders like those in winamp are very basic though.
Though this codec is suppose to play allright with standard mp3 decoders,
maybe the decoders that don't work are non-standard ?