QAudioOutput constructor hangs in PyQt6

[Phil Thompson]

It's not clear from your description as to exactly what's happening and 
what you expect to happen. Also your Python and C++ code are not 
equivalent as they interact with the event loop in different ways.

Phil

On 09/04/2026 15:30, ekhumoro wrote:
> Hello
> 
> I have encountered some problems when creating an instance of
> QAudioOutput in PyQt6, which result in the program hanging without
> producing any error messages. I am testing on Linux using PyQt-6.11.0
> / Sip-6.15.2, although I suspect the issue may be difficult to
> reproduce on other platforms. However, it seems reasonable to assume
> PyQt6 must be at least partly responsible, as an equivalent C++
> example doesn't show any of the problematic behaviours. Any insights
> regarding the cause of this rather strange issue would be gratefully
> received.
> 
> The two examples are given below. Note that it's not really necessary
> to try to play an audio file.
> 
> PyQt6 example:
> 
>     #!/usr/bin/python3
> 
>     import sys, signal
>     signal.signal(signal.SIGINT, signal.SIG_DFL)
>     print('Press Ctrl+C to quit\n')
> 
>     from PyQt6.QtCore import (
>         qInstallMessageHandler, QUrl, QTimer, QtMsgType, qDebug
>         )
>     from PyQt6.QtWidgets import QApplication
>     from PyQt6.QtMultimedia import QMediaPlayer, QAudioOutput
> 
>     def messageHandler(mode, context, message):
>         if mode == QtMsgType.QtInfoMsg:
>             print(f'INFO: {message}\n')
>         elif mode == QtMsgType.QtDebugMsg:
>             print(f'DEBUG: {message}\n')
>         elif mode == QtMsgType.QtWarningMsg:
>             print(f'WARNING: {message}\n')
>         elif mode == QtMsgType.QtCriticalMsg:
>             print(f'CRITICAL: {message}\n')
>         elif mode == QtMsgType.QtFatalMsg:
>             print(f'FATAL: {message}\n')
> 
>     # PyQt6 hangs with a message-handler set, unlike C++
>     # qInstallMessageHandler(messageHandler)
> 
>     app = QApplication(['Test'])
> 
>     def main():
>         global player, audio
>         player = QMediaPlayer()
>         qDebug('creating audio output...')
>         audio = QAudioOutput()
>         qDebug('audio output created')
>         qInstallMessageHandler(messageHandler)
>         player.setAudioOutput(audio)
>         if len(sys.argv) > 1:
>             player.setSource(QUrl.fromLocalFile(sys.argv[1]))
>             player.play()
>         else:
>             qDebug("cancelled: no audio source provided")
>             app.quit()
> 
>     # PyQt6 hangs without the following, unlike C++
>     # QTimer.singleShot(100, main)
>     main()
> 
>     app.exec()
> 
> C++ example:
> 
>     #include <QDebug>
>     #include <QTimer>
>     #include <QApplication>
>     #include <QMediaPlayer>
>     #include <QAudioOutput>
>     #include <QtLogging>
>     #include <QMessageLogContext>
>     #include <QString>
> 
>     void messageHandler(QtMsgType type, const QMessageLogContext &,
> const QString &str)
>     {
>         const char * msg = qPrintable(str);
>         switch (type)
>         {
>             case QtInfoMsg:
>                 fprintf(stderr, "INFO: %s\n\n", msg);
>                 break;
>             case QtDebugMsg:
>                 fprintf(stderr, "DEBUG: %s\n\n", msg);
>                 break;
>             case QtWarningMsg:
>                 fprintf(stderr, "WARNING: %s\n\n", msg);
>                 break;
>             case QtCriticalMsg:
>                 fprintf(stderr, "CRITICAL: %s\n\n", msg);
>                 break;
>             case QtFatalMsg:
>                 fprintf(stderr, "FATAL: %s\n\n", msg);
>                 abort();
>         }
>     }
> 
>     int main(int argc, char *argv[])
>     {
>         qInstallMessageHandler(messageHandler);
> 
>         QApplication app(argc, argv);
> 
>         QMediaPlayer *player = new QMediaPlayer;
>         qDebug("creating audio output...");
>         QAudioOutput *audioOutput = new QAudioOutput;
>         qDebug("audio output created");
>         player->setAudioOutput(audioOutput);
>         if (argc > 1) {
>             QUrl source = 
> QUrl::fromLocalFile(QApplication::arguments().at(1));
>             player->setSource(source);
>             qDebug() << "source url: " << player->source();
>             player->play();
>             QTimer::singleShot(15000, app.quit);
>             app.exec();
>         } else {
>             qInfo() << "cancelled: no source file provided";
>         }
>     }