How to run QSoundEffect or QMediaPlayer in a loop that is in a thread?

Question

The problem is that I am unable to play sound from a thread using QSoundEffect or QMediaPlayer . The only way that I got it to play sound once per program start is when I added:

QEventLoop loop;
loop.exec();

But this approach does not fit my need since I need the sound to be able to play more than once. Infinite loop count not what I need, but when used sound is played repeatedly til I end the program. No errors with neither of my approaches. So, what am I missing or using not the correct way?

By the way QSound works but I can't control loop count and volume with that, so I'm trying to get QSoundEffect or QMediaPlayer to work since they have this ability.

// main.cpp

QThread sound_thread;
QTimer sound_loop_timer;
Sound sound;
QObject::connect(&sound_loop_timer, SIGNAL(timeout()), &sound, SLOT(exec()));
sound_loop_timer.start(500);
sound_loop_timer.moveToThread(&sound_thread);
sound.moveToThread(&sound_thread);
sound_thread.start();

// Sound.h

class Sound : public QObject
{
    Q_OBJECT
public:
    Sound();

private slots:
    void exec();

private:
    void playSound();
    QSoundEffect *sound_effect;

};

// Sound.cpp

Sound::Sound()
{

}

void Sound::exec(){
    //...
    playSound();
}
void Sound::playSound(){
    sound_effect = new QSoundEffect;
    sound_effect->setSource(QUrl("qrc:/sounds/audio/test.wav"));
//    sound_effect->setLoopCount(QSoundEffect::Infinite);
    sound_effect->setVolume(0.9);
    sound_effect->play();
//  QEventLoop loop;
//  loop.exec();

    QMediaPlayer player;// = new QMediaPlayer;
    player.setMedia(QUrl::fromLocalFile("/home/path/audio/test.wav"));
    player.setVolume(50);
    player.play();
    QEventLoop loop;
//  loop.exec();
//  loop.exit();
}

Answer 1

You don't have to handle the event loop by yourself since the default implementation of QThread::run() do it for you.

I have made a simple example that plays a sound using QSoundEffect in another thread.

As I was not sure about what exactly you want to do, I assumed the following statements:

• A SoundHandler will handle the QSoundEffect object.
• On click on the start button, the sound is played in a separate thread.
• The sound is played with an infinite loop and is stopped after the timeout of a timer.

The below code is only meant to show you how to play a sound in a separate thread (what you asked for). If the above specifications does not fit the requirements of your use case, I think you can easily adapt the code to make it suit your needs.

test.h :

#ifndef TEST_H
#define TEST_H

#include <QMainWindow>
#include <QPushButton>
#include <QSoundEffect>
#include <QTimer>
#include <QThread>

class SoundHandler final : public QSoundEffect
{
    Q_OBJECT

    private:
        QTimer * life_time_handler;

    public:
        SoundHandler(const QUrl & sound_path, int life_time_ms, QObject * parent = nullptr);

    public slots:
        void playSound();
        void stopSound();

    signals:
        void hasFinished();
};

class TestWindow : public QMainWindow
{
    Q_OBJECT

    protected:
        QPushButton * start_sound_thread;
        QThread sound_thread;
        SoundHandler * sound_effect;

    public:
        TestWindow();
        ~TestWindow();
};

#endif // TEST_H

test.cpp :

#include "test.h"

#include <QApplication>

SoundHandler::SoundHandler(const QUrl & sound_path, int life_time_ms, QObject * parent) : QSoundEffect(parent)
{
    setSource(sound_path);
    setVolume(0.5);
    setLoopCount(QSoundEffect::Infinite);
    life_time_handler = new QTimer(this);
    life_time_handler->setInterval(life_time_ms);
    life_time_handler->setSingleShot(true);

    connect(life_time_handler, &QTimer::timeout, this, &SoundHandler::stopSound);
}
void SoundHandler::playSound()
{
    life_time_handler->start();
    play();
}
void SoundHandler::stopSound()
{
    stop();
    emit hasFinished();
}

TestWindow::TestWindow()
{
    start_sound_thread = new QPushButton("Start");
    this->setCentralWidget(start_sound_thread);

    sound_effect = new SoundHandler(QUrl::fromLocalFile("../test/audio/test.wav"), 4000);
    sound_effect->moveToThread(&sound_thread);
    connect(&sound_thread, &QThread::finished, [&](){sound_effect->deleteLater();});
    connect(&sound_thread, &QThread::started, sound_effect, &SoundHandler::playSound);

    // Handle the thread termination
    connect(sound_effect, &SoundHandler::hasFinished, [&](){
        sound_thread.quit();
        sound_thread.wait();
    });

    // Handle the thread launch
    connect(start_sound_thread, &QPushButton::clicked, [&](){
        sound_thread.start();
        start_sound_thread->setEnabled(false);
    });
}
TestWindow::~TestWindow()
{
    if(sound_thread.isRunning())
    {
        sound_thread.quit();
        sound_thread.wait();
    }
}

int main(int argc, char ** argv)
{
    QApplication app(argc, argv);

    TestWindow tw;
    tw.show();

    return app.exec();
}

I've tested it and it worked fine.

Notes:

• I choosed here to make the SoundHandler a subclass of QSoundEffect for convenience purposes but it is not required (it could have a QSoundEffect object as a member instead of subclassing it).
• The TestWindow contains only a single QPushButton to launch the sound in a separate thread. Once launched, the button becomes disabled.

I hope it helps.