about mxj~ MSPBuffer poke method (and VBR mp3 lengths)

A long long long long long long time ago, Ali Momeni wanted to play
with mp3's and mxj.

There http://www.synthesisters.com/hypermail/max-msp/Nov05/34373.html
He wrote :
"however, i'm having trouble setting the length of a buffer because
the getFrameLength() method of an AudioInputStream seems to always
return -1 (!@#$)."

And there were no answers. I wanted to give you the result of my
searches about this specific subject:

1- Indeed, normal getFrameLength() does not give the length of an
audiostream coming from an mp3. It exists a trick to calculate the
mp3 length from the file information. However this is useless because
you will anyway get problems with VBR mp3s...

2- It _seems_ (not 100% sure) the real trick is to use
javazoom.jl.decoder.* ( http://www.javazoom.net/javalayer/
sources.html ) as follow :

import javazoom.jl.decoder.*;
...........

int nTotalMS = 0;

try {
Bitstream m_bitstream = new Bitstream(new FileInputStream
(your_file));
Header m_header = m_bitstream.readFrame();

int mediaLength = (int)encodedFile.length();

if (mediaLength != AudioSystem.NOT_SPECIFIED) {
nTotalMS = Math.round(m_header.total_ms(mediaLength));
            }
post("Length in ms: " + nTotalMS);
} catch(Exception e) {
e.printStackTrace();
    }
}

Best,
O./