QAudioDeviceInfo::defaultOutputDevice() is incorrectly null

ThomH

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?

Bonnie

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