java - 如何使用 Java 解析 midi 的速度？

Question

我不明白如何跟上节奏。 所以仍然使用一些糟糕的方式来使用我的输出速度。

我真的认为只使用 NOTE_ON 和 NOTE_OFF 计时就能给我实时。 但是这个输出在 C++ 中仍然播放得太慢。

附言
演奏时我们只使用一个 VOICE midis。 (这只是为了好玩，我们教室里的一些电脑正在同步播放一些 2+ VOICE 音乐)。

这是我的代码:

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 文件使用两个值来指定时间，分辨率(以每四分音符的节拍为单位)和节奏(以每四分音符的微秒为单位)。

可以从 Sequence 中读取分辨率。 .

速度由 MIDI 消息指定；您必须在第一首轨道中搜索 SET_TEMPO 元事件，这会更改所有后续事件的速度，直到下一个速度事件。

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