Java Tritunous MP3Encodeは簡単

すごく簡単に、lame_enc.dll呼び出せたよ。
http://www.tritonus.org/plugins.html

引数は以下な感じです。
Mp3Encoder - convert audio files to mp3 (layer III of MPEG 1, MPEG 2 or MPEG 2.5
java Mp3Encoder [...]
The output file(s) will be named like the source file(s) but
with mp3 file extension.

You need LAME 3.88 or later. Get it from http://sourceforge.net/projects/lame/

may be a combination of the following:

• q Quality of output mp3 file. In VBR mode, this affects

the size of the mp3 file. (Default middle)
One of: lowest, low, middle, high, highest

• b Bitrate in KBit/s. Useless in VBR mode. (Default 128)

One of: 32 40 48 56 64 80 96 112 128 160 192 224 256 320 (MPEG1)
Or: 8 16 24 32 40 48 56 64 80 96 112 128 144 160 (MPEG2 and MPEG2.5

• V VBR (variable bit rate) mode. Slower, but potentially better

quality. (Default off)

• v Be verbose.
• s Be silent.
• e Debugging: Dump stack trace of exceptions.
• t Debugging: trace execution of converters.
• h | --help Show this message.