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QAudioDeviceInfo::defaultOutputDevice() is incorrectly null

  • I am building code I wrote myself under Ubuntu 20.04 in Qt Creator 4.11.0 which reports itself as being based on Qt 5.12.8. I'm running this under VMWare. I installed Qt Creator via its Snap, as presented in the 'Ubuntu Software' storefront.

    The 'Settings' application shows a sound output device (of Analog Output - ES1371/ES1373 / Creative Labs CT2518 (Audio PCI 6V/128/5200 / Creative CT4810/CT5803/CT5806 [Sound Blaster PCI]), though of course that's just what VMWare is presenting to the virtualised machine). If I hit the 'Test' button and play some of the tests, they are audible.

    If I launch Firefox and browse to e.g. Youtube then it also has no problem producing sound.

    Tracking down an issue with the Linux build of my Qt project, I added the following slightly redundant code:

    qDebug() << "Available devices:" << QAudioDeviceInfo::availableDevices(QAudio::AudioOutput).size();
    const QAudioDeviceInfo &defaultDeviceInfo = QAudioDeviceInfo::defaultOutputDevice();
    if(defaultDeviceInfo.isNull()) {
        qDebug() << "No default device";

    And it dutifully outputs:

    Available devices: 0
    No default device

    Is there anything I can do to look behind that? Why is Qt unable to find an audio device when I clearly have one, and Firefox has no issue taking advantage of it? Is this normal for Qt under X11?

  • Does the audio plugins also be installed by Ubuntu?
    On Linux, there should be plugins/audio/ and plugins/audio/
    Also, from their name, you can know that they use alsa and pulseaudio as backends.
    Do you have either of the libraries installed too?

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