QtMultimedia, QAudioInput, default device: volume() and setVolume() don't work as expected

#include <iostream>
#include <QAudioInput>

using namespace std;

int main()
{
    QAudioInput* audio;
    {
        QAudioFormat format;
        // Set up the desired format, for example:
        format.setSampleRate(8000);
        format.setChannelCount(1);
        format.setSampleSize(8);
        format.setCodec("audio/pcm");
        format.setByteOrder(QAudioFormat::LittleEndian);
        format.setSampleType(QAudioFormat::UnSignedInt);

        QAudioDeviceInfo info = QAudioDeviceInfo::defaultInputDevice();
        if (!info.isFormatSupported(format)) {
            cout << "Default format not supported, trying to use the nearest.";
            format = info.nearestFormat(format);
        }

        audio = new QAudioInput(format);

        qreal v0 = audio->volume();
        cout << "v0 = " << v0 << endl; // v0 is always 0.0

        audio->setVolume(qreal(0.5));
        qreal v1 = audio->volume();
        cout << "v1 = " << v1 << endl; // v1 is always 0.0 (should be 0.5)
    }
}