midi.sequencer中的序列何时结束？

mum43rcc 于 2021-07-03 发布在 Java

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有这样一个简单的代码可以工作（但直到我用^-c终止它，它才结束）：

import javax.sound.midi.*;

public class Foo {

    public void play(int instrument, int note) {
        try {
            Sequencer player = MidiSystem.getSequencer();
            player.open();

            Sequence seq = new Sequence(Sequence.PPQ, 4);
            Track track = seq.createTrack();

            ShortMessage first = new ShortMessage();
            first.setMessage(192, 1, instrument, 0);
            MidiEvent changeInstrument = new MidiEvent(first, 1);
            track.add(changeInstrument);

            ShortMessage a = new ShortMessage();
            a.setMessage(144, 1, note, 100);
            MidiEvent noteOn = new MidiEvent(a, 1); //fired on "tick 1"
            track.add(noteOn);

            ShortMessage b = new ShortMessage();
            b.setMessage(128, 1, note, 100);
            MidiEvent noteOff = new MidiEvent(b, 8); //fired on "tick 8"
            track.add(noteOff);

            player.setSequence(seq);
            player.start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Foo foo = new Foo();
        foo.play(0, 42); 
    }
}

这个
noteOn MidiEvent 向…开火 1 tick （第二个论点） MidiEvent 构造函数）。这个
noteOff MidiEvent 向…开火 8 tick ，也就是说。应该有7个刻度。但我永远看不到结局。当从cmd触发时，提示永远不会返回，除非我强制进程终止（使用 <ctrl-c> ). 为什么？音序器什么时候结束，程序什么时候结束？
编辑：这可能是由于打开序列器，但没有关闭它。所以我想在最后关闭它，但它不能立即跟随 player.start() 声明，否则立即结束。所以一定有耽搁。不过，这是一个笨拙的解决方案

...
        player.setSequence(seq);
        player.start();
        TimeUnit.SECONDS.sleep(3);
        player.close();

之后，提示返回。但是有更好的解决办法吗？

Java Duration midi javax.sound.midi

来源：https://stackoverflow.com/questions/65174404/when-does-the-sequence-from-midi-sequencer-ends

2条答案

按热度按时间

rkkpypqq1#

当sequencer#isrunning（）等于 false . 我想你应该先关闭sequencer对象再开始另一个序列。将sequence对象声明为类成员可以提供更多的灵活性：

// Declare Sequencer as a class member variable and initialize to null.
javax.sound.midi.Sequencer sequencer = null;

public void playMidi(String midiFilePath) {
    // Prevent a new Midi audio file is one is already playing.
    if (sequencer != null) {
        // If sequncer is running get outta here.
        if (sequencer.isRunning()) { 
            return; 
        }
        // Otherwise close the sequencer.
        else { 
            sequencer.close(); 
        }
    }
    // Play the Midi file in its own thread.
    Thread newThread = new Thread(() -> {
        try {
            // Obtains the default Sequencer connected to the System's default device.
            sequencer = javax.sound.midi.MidiSystem.getSequencer();

            // Opens the device, indicating that it should now acquire any
            // system resources it needs and becomes operational.
            if (sequencer.isRunning()) {
                return;
            }
            sequencer.open();

            // Stream in a Midi file
            java.io.InputStream is = new java.io.BufferedInputStream(new java.io.FileInputStream(new File(midiFilePath)));

            // Sets the current sequence on which the sequencer operates.
            // The stream must point to MIDI file data.
            sequencer.setSequence(is);
            is.close();
            // Starts playback of the MIDI data in the currently loaded sequence.
            sequencer.start();
        }
        catch (MidiUnavailableException | IOException | InvalidMidiDataException ex) {
            Logger.getLogger("playMidi() Method Error!").log(Level.SEVERE, null, ex);
        }
    });
    newThread.start();
}

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lnxxn5zx2#

您需要添加metaeventlistener来捕获“序列结束”事件：

player.addMetaEventListener(metaEvent ->
        {
            if (metaEvent.getType() == 47) // end of sequence
            {
                player.stop();  // Not mandatory according to API doc, but better to have it

                // This is called from the Sequencer thread, NOT from the EDT
                // So we need SwingUtilities if we want to update the UI
                Runnable doRun= new Runnable()
                {
                    @Override
                    public void run()
                    {
                        doSomethingAfterStop();
                    }
                };
                SwingUtilities.invokeLater(doRun);
            }
        });

如果您只想在序列结束时退出程序，只需直接调用侦听器中的system.exit（）。
请注意，如果使用sequencer.setloopcount（x）且x>0，则永远不会调用序列结束侦听器，您将需要一个ui按钮（或计时器）来触发对sequencer.stop（）的调用。
在使用java sequencer时，有一些技巧需要了解，如果您需要示例代码，请查看我在github上的应用程序jjazzlab-x，尤其是 MusicController.java 在 MusicController 模块。

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midi.sequencer中的序列何时结束？

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