Using QAudioOutput as Input

[Wolfspirit]

Hello. I want to record audiooutput into a .wav-file. All I got is a empty file. Here is my code:

QAudioOutput *my_audioOutput = new QAudioOutput();
QMediaCaptureSession *my_session = new QMediaCaptureSession();
QMediaRecorder *my_recorder = new QMediaRecorder();
bool recording = false;
...
...
...
void MainWindow::on_pushButtonRecord_clicked()
{
    if(recording == true) {
        my_recorder->stop();
        recording = false;
    }
    else {
        // RECORD
        my_audioInput = new QAudioInput();
        my_audioInput->setDevice(my_audioOutput->device());    // <-- This does not work
        my_session->setAudioInput(my_audioInput);
        my_session->setRecorder(my_recorder);
        my_recorder->setMediaFormat(QMediaFormat::Wave);
        my_recorder->setOutputLocation(QUrl::fromLocalFile("/home/thomas/Projects/mymp3player/test"));
        my_recorder->setAudioSampleRate(48000);
        my_recorder->setAudioChannelCount(2);
        my_recorder->record();
        recording = true;
    }
}

Can someone help me on this?

[Wolfspirit]

Seems like I have to change the input device via pavucontrol:
Audio Loopback Recording with PulseAudio

But I don't want to do this every time manually for my application. There must be some way to do this in QT.......

[Bonnie]

@Wolfspirit said in Using QAudioOutput as Input:

There must be some way to do this in QT.......

What Qt can do is to just open and read your existing audio input devices.
If your system has a loopback input device, then Qt can open it. If not then Qt can't.

I don't use linux often but I remember having loopback-like ones when printing the names of all the audio input devices using Qt, not sure this is soundcard-related or not. So maybe you can first try listing the input devices using Qt to see if there's one.

If there's not, as I googled, this loopback thing can be set by command line (reference: https://forums.debian.net/viewtopic.php?t=110440 or https://huma.id/pa-loopback/). But that has nothing to do with Qt. You can make Qt to run a command script before opening the device if you find out how to set that by script.

[Wolfspirit]

@Bonnie This... is... great! Thank you very much.
I came up with following commands:

pactl load-module module-null-sink sink_name=my_sink_mix sink_properties=device.description=my_sink_mix
pactl load-module module-loopback latency_msec=60 adjust_time=6 source=alsa_output.pci-0000_00_1b.0.analog-stereo.monitor sink=my_sink_mix
pactl load-module module-remap-source master=my_sink_mix.monitor source_name=vmic source_properties=device.description=virtual_mic

So, all I have to do is to write something with QProcess with these commands. And then use "vmic" as QAudioInput and "my_sink_mix" as QAudioOutput and voila! I can hear the audiostream and save it to disc simultaneously.

Again: Thank you very much!