Qt Recording audio with MediaRecorder on android doesn't work

Question

I want to record and save audio in a file. Here is the code is use:

QAudioEncoderSettings audioSettings;
audioSettings.setCodec("audio/pcm");
audioSettings.setQuality(QMultimedia::HighQuality);

audioRecorder.setEncodingSettings(audioSettings);
dir = QStandardPaths::standardLocations(QStandardPaths::HomeLocation).value(0);

QString qdir = dir.path();
qdir.append(QString("/test.wav"));

audioRecorder.setOutputLocation(QUrl::fromLocalFile(qdir));

audioRecorder.record();

This works perfectly fine on windows. I can record, save and play the sound without any problems. As soon as i try this code on androind i get:

D MediaRecorder: getMaxAllowedFileSizeByPath

D MediaRecorder: no match storage volume found!

I set the required storage and record permissions. The phone i am trying to run the code on is a HTC one M8 (Anroid version 6.0)

I tried to create a file manually, but this doesn't work either.

QDir folder = QStandardPaths::writableLocation(QStandardPaths::DocumentsLocation);

QString qdir = folder.path();
qdir.append(QString("/transmission.wav"));
QFile file(qdir);

if (file.exists())
  file.remove();

qDebug() << "file exists:  " << file.exists();

if (!file.exists()) {

    if (!folder.exists()) {
        folder.mkpath(folder.path());
    }

    file.open(QIODevice::WriteOnly);
    file.write("Hello World");
    file.close();
}
if (file.exists()) {
    qDebug() << "file exists:  " << file.exists();
    file.open(QIODevice::ReadOnly);
    QByteArray data=file.readAll();
    qWarning("file data=%s",data.constData());
    file.close();
}

QStandardPaths::writableLocation(QStandardPaths::DocumentsLocation) gives back: storage/0/emulated/Documents

file.open(QIODevice::ReadOnly) gives back QIODevice::write (QFile, "/storage/emulated/0/Documents/transmission.wav"): device not open

Looks like the recorder is not able to create a file - nor am i.