@Anthony-Abboud for the crackling sound issue, I could fix my issues with https://codereview.qt-project.org/c/qt/qtmultimedia/+/503818 and this is such a generic error that I expect that you hit the same problem.
For the missing sound output, the following changed helped me https://codereview.qt-project.org/c/qt/qtmultimedia/+/503819 . Yet for that I am not sure yet if it is a proper solution or just a workaround.

Hi @robcreamer, this is outside my expertise, but I suggest you subscribe to the Interest mailing list (http://lists.qt-project.org/mailman/listinfo/interest ) and post your sample code + 122.7-hour log there. I'm sure one of the Qt engineers on the list can tell you what's happening.

@SGaist

Huge thanks for the shared link :)

Topic->setAsClosed(true);

@nekkceb Further debugging FINALLY found the absurdly simple problem: I did not have the qtaudio_windows.dll files in my plugins/audio folder! That's it! Finally discovered single-stepping into

void QFactoryLoader::update()