How can I parse a tempo of midi using Java?

Question

I do not understand how to catch tempo. So still use some shitty way to use tempo to my output.

I really thinks that just using NOTE_ON & NOTE_OFF timings will give me real time. But this output still played too slow in C++.

P.S.
We use only ONE VOICE midis when playing that. (It's just for fun, some computers in our class room is playing some 2+ VOICE music synchronized).

Here is my code:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import javax.sound.midi.*;
import javax.swing.*;
import javax.swing.filechooser.FileNameExtensionFilter;
import static java.lang.Math.*;

public class MidiReader {
    public static final float DEFAULT_TEMPO = 100.0f;
    public static final int NOTE_ON = 0x90;
    public static final int NOTE_OFF = 0x80;
    public static final float[] NOTES = {32.70f, 34.65f, 36.95f, 38.88f, 41.21f, 43.65f,
            46.25f, 49.00f, 51.90f, 55.00f, 58.26f, 61.74f};
    private JFrame frame = new JFrame();
    private JTextArea outText = new JTextArea();
    private JPanel panel = new JPanel();
    private File inputFile = null;
    private JButton button = new JButton("Choose file");
    private JTextField inputTempo = new JTextField(Integer.toString((int) DEFAULT_TEMPO));
    private float tempo = DEFAULT_TEMPO;

    public void init(){
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 400);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setLayout(new BorderLayout());
        panel.setLayout(new BorderLayout());
        panel.add(outText, BorderLayout.CENTER);
        panel.add(inputTempo, BorderLayout.SOUTH);
        frame.add(panel, BorderLayout.CENTER);
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                JFileChooser fileopen = new JFileChooser();
                FileNameExtensionFilter filter = new FileNameExtensionFilter(
                        "Midi files", "mid");
                fileopen.setFileFilter(filter);
                int ret = fileopen.showDialog(null, "Choose File");
                if (ret == JFileChooser.APPROVE_OPTION) {
                    inputFile = fileopen.getSelectedFile();
                }
                if (inputFile != null) {
                    setTempo(Float.parseFloat(inputTempo.getText()));
                    outText.setText("");
                    calculate(getTempo());
                }
            }
        });
        inputTempo.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                setTempo(Float.parseFloat(inputTempo.getText()));
                outText.setText("");
                calculate(getTempo());
            }
        });
        frame.add(button, BorderLayout.SOUTH);
        frame.setTitle("Midi to C++ Beep");

    }

    public void setTempo(float tempo) {
        this.tempo = tempo;
    }

    public float getTempo(){
        return this.tempo;
    }

    public float getPitch(int key){
        return NOTES[key % 12] * (float) (pow(2.0, (key / 12) - 2));
    }

    public MidiReader(){
        init();
    }


    public void calculate(float tempo){
        Sequence sequence = null;
        try {
            sequence = MidiSystem.getSequence(inputFile);
        } catch (InvalidMidiDataException e) {
            System.exit(0);
        } catch (IOException e) {
            e.printStackTrace();
        }

        for (Track track :  sequence.getTracks()) {
            int key;
            long startTime = 0;
            long stopTime;
            for (int i = 0; i < track.size(); i++) {
                MidiEvent event = track.get(i);
                MidiMessage message = event.getMessage();
                if (message instanceof ShortMessage) {
                    ShortMessage sm = (ShortMessage) message;
                    switch(sm.getCommand()){
                        case NOTE_ON:
                            startTime = event.getTick();
                            break;
                        case NOTE_OFF:
                            stopTime = event.getTick();
                            key = sm.getData1();
                            outText.append(
                                "\t" + "Beep(" + getPitch(key) + ", " +
                                (int)((stopTime - startTime) * (DEFAULT_TEMPO / tempo)) + ");" + "\n");
                            break;
                    }
                }
            }
        }
    }

    public static void main(String[] args){
    new MidiReader();
}
}

Answer 1

MIDI files use two values to specify the timing, the resolution (measured in ticks per quarter note), and the tempo (measured in microseconds per quarter note).

The resolution can be read from the Sequence.

The tempo is specified with MIDI messages; you have to search the first track for SET_TEMPO meta events, which change the tempo for all following events until the next tempo event.

Also see How to get integer value from byte array returned by MetaMessage.getData()?, How does Midi TEMPO message apply to other tracks?, and Reading notes from MIDI file using NAudio.