packMP3 is a compression program specially designed for further compression of MPEG-1 Audio Layer III audio files without causing any further loss. It works the same as my more popular other compression software packJPG and typically reduces the file size of a MP3 file by 16% based on tests with 6000 randomly selected files.

Download it from here:
packMP3 v1.0g (LGPL)

packMP3 includes source code and is open source under the GPL.

There are no known bugs for packMP3, meaning that it can be considered stable software. Always be careful, though, and never delete any original files without at least having verified the compressed files’ integrity (option -v).

There’s also a third party graphical user interface for packMP3:
packMP3 Options by Michael Lee


  1. mman says:

    Hi, that is interesting compressor.
    I tested it and saw next:
    – it works good without any bugs;
    – compression ratio is good, but old “soundslimmer” library compress mp3 files better (a little);
    – it does not work when sample rate is 22 khz for example.
    Anyway, it’s good project. I’ll glad to test future versions (I hope, they get here). Good luck.
    PS. Sorry for my broken English 🙂

  2. j7n says:

    This compressor works well on the output of the Fraunhofer encoder which uses only simple stereo at 320 kbit/s and leaves about 50 kbit/s of padding. A mono encode is reduced to about 40% of source and ~50% compared with mp3packer (which is only able to remove the padding). Near mono encodes are also reduced significantly.

    I don’t know the compression internals. Why isn’t the Huffman stage of standard MP3 able to remove redundancy between 2 identical channels?

    • Matthias Stirner says:

      MP3 Huffman compression actually handles each channel separately. There is no reduction of redundancy between the channels.

Leave a Reply

Your email address will not be published. Required fields are marked *