java - Get decoded byte stream from MP3 file -

i want fft on mp3 file. this, extract decoded byte stream file format (i believe called raw pcm data).for task using jlayer 1.0.1 library. here code should extract pcm data each frame:

        short[] pcmout = {};         bitstream bitstream = new bitstream(new fileinputstream(path_to_mp3_file));         boolean done = false;         while (!done) {             header frameheader = bitstream.readframe();             if (frameheader == null) {                 done = true;             } else {                 decoder decoder = new decoder();                 samplebuffer output = (samplebuffer) decoder.decodeframe(bitstream.readframe(), bitstream); //returns next 2304 samples                 short[] next = output.getbuffer();                 pcmout = concatarrays(pcmout, next);                 //do whatever samples             }             bitstream.closeframe();         }         (int = 0; < pcmout.length; i++) {             if (pcmout[i] != 0) {                 system.out.println(pcmout[i]);             }         } 

the problem variable short[] pcmout filled zeros valid mp3 file. root cause of such problem?

checking seems related decoder; apart waste create new decoder each time seems fundamental problem in implementation seems return first frame while constant decoder seems keep track:

decoder decoder = new decoder(); while (!done) {   header frameheader = bitstream.readframe();   if (frameheader == null) {             done = true;   }   else {      samplebuffer output = (samplebuffer) decoder.decodeframe(frameheader, bitstream);             short[] next = output.getbuffer();             for(int i=0; i<next.length; i++) system.out.print(" "+next[i]);             pcmout = concatarrays(pcmout, next);             //do whatever samples   }