Do you have a program that plays one song, yet? If not, then that's where to start... Implementing what you have in mind is as simply as looping over the load and play code.

see

[EDITED]

https://forum.processing.org/topic/lovely-mp3-player

I just solved the problem. For those who will have the same problem.

Processing code (the path is only for mac users), the programm plays the songlist from desktop and shows a 8-band EQ. If you want to drive Led as a 7 band EQ just send the val2 to arduino

import ddf.minim.*;
import ddf.minim.analysis.*;
AudioPlayer[] player = new AudioPlayer[4];
Minim minim;
FFT fft;
float val;
int val2;
int bufferSize = 8;
int fftSize = floor(bufferSize*.9)+1;
int count=0;


void setup() {
  size(600, 260);

  minim = new Minim(this);
  player[0] = minim.loadFile("/Users/.../Desktop/m.mp3");
  player[1] = minim.loadFile("/Users/.../Desktop/Y.mp3");
  player[2] = minim.loadFile("/Users/.../Desktop/t.mp3");
  player[3] = minim.loadFile("/Users/.../Desktop/h.mp3");


  player[count].play();

  fft=new FFT(player[count].bufferSize(), player[count].sampleRate());
}

void draw()
{
  if(!player[count].isPlaying())
  {
    count++;
    if(count>3)count=0;
    player[count].play();   
  }
   
  fft.forward(player[count].mix);
  background(255);

  for (int i = 0; i < fftSize; i++)
  {
    float band = fft.getBand(i);
    float control,afactor=10;
    control=band*afactor;
    if(control>1023)control=1023;
   
      val=map(control, 0, 1023, 0, 255);
      val2=int(val);

      print("chanel ");
      print(i);
      print("  actual value ");
      print(val2);
      println();

      fill(0);
      ellipse(5+i*(width/8), height-val2, 10, 10);

      }
    line(0, height-255, width,height-255);

}
void stop()
{
  //player.close();
  //minim.stop();
 // super.stop();
}