Solved QAudioInput: failed to open audio device

[asdlkjqpwoei]

I'm try to use Qt Multimedia to open microphone and access data. I followed the official Audio Input Example and get the following code(Just a test program, I will inject into my other project when it's okay).
Environment: Windows 10 20H2. Qt Creator, MinGW 64-bit or Microsoft Visual Studio 2019, MSVC2019 64-bit.

#include "main_window.h"
#include "ui_main_window.h"
MainWindow::MainWindow(QWidget* parent): QMainWindow(parent), ui(new Ui::MainWindow), AvailableAudioInputDevices(QAudioDeviceInfo::availableDevices(QAudio::AudioInput)), Microphone(nullptr), MicrophoneStream(nullptr)
{
    ui->setupUi(this);
    /* List all devices */
    ui->OutputTextBrowser->setPlainText(QString::fromUtf8("Available audio input devices:"));
    for(int i=0;i<AvailableAudioInputDevices.size();i++)
    {
        ui->OutputTextBrowser->append(AvailableAudioInputDevices.at(i).deviceName());
    }
    /* Set up data format */
    DataFormat.setSampleSize(16);
    DataFormat.setSampleRate(16000);
    DataFormat.setCodec(QString("audio/pcm"));
    DataFormat.setSampleType(QAudioFormat::Float);
    DataFormat.setByteOrder(QAudioFormat::LittleEndian);
    DataFormat.setChannelCount(2);
    /* Check format supported */
    if(QAudioDeviceInfo::defaultInputDevice().isFormatSupported(DataFormat))
    {
        ui->OutputTextBrowser->append(QString::fromUtf8("Supported format."));
    }
    else
    {
        ui->OutputTextBrowser->append(QString::fromUtf8("Unsupported format."));
    }
    /* Open */
    Microphone.reset(new QAudioInput(QAudioDeviceInfo::defaultInputDevice(), DataFormat));
    MicrophoneStream.reset(Microphone->start());
}

I got the output from the text browser.

Available audio input devices:
Microphone Array (Realtek(R) Audio)
Stereo Mix (Realtek(R) Audio)
Supported format.

Output from the debug console.

QAudioInput: failed to open audio device

Of course my program can't work but the example work properly.
I found some possible cause from Google but none work such as turning on Windows 10 privacy setting. The problem has block me a couple of days and I still get no idea.

[SGaist]

Hi and welcome to devnet,

What I would check is the exact differences you have with regard to the example.

One silly question, do you have another application using the same device ?

[asdlkjqpwoei]

@SGaist No other applications use the device when I debug.

[SGaist]

When exactly does the error happen ? Already in the constructor ?

[asdlkjqpwoei]

@SGaist All I got only QAudioInput: failed to open audio device no matter where it is. I try to start() at other function or active through the signals&slots but got the same issue. QAudioInput::error() return 1(QAudio::OpenError).

[asdlkjqpwoei]

This is the complete test program code.

/* main_window.h */
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QAudioDeviceInfo>
#include <QAudioFormat>
#include <QAudioInput>
#include <QIODevice>
#include <QMainWindow>
QT_BEGIN_NAMESPACE
namespace Ui
{
    class MainWindow;
}
QT_END_NAMESPACE
class MainWindow: public QMainWindow
{
    Q_OBJECT
    private:
        /* User interferace */
        Ui::MainWindow *ui;
        /* Multimedia */
        const QList<QAudioDeviceInfo> AvailableAudioInputDevices;
        QAudioFormat DataFormat;
        QAudioInput* Microphone;
        /* IO stream */
        QIODevice* MicrophoneStream;
    public:
        MainWindow(QWidget *parent = nullptr);
        ~MainWindow();
};
#endif // MAINWINDOW_H

// ---------------------------------------

/* main_window.cpp */
#include "main_window.h"
#include "ui_main_window.h"
MainWindow::MainWindow(QWidget* parent): QMainWindow(parent), ui(new Ui::MainWindow), AvailableAudioInputDevices(QAudioDeviceInfo::availableDevices(QAudio::AudioInput)), Microphone(nullptr), MicrophoneStream(nullptr)
{
    ui->setupUi(this);
    /* List all devices */
    ui->OutputTextBrowser->setPlainText(QString::fromUtf8("Available audio input devices:"));
    for(int i=0;i<AvailableAudioInputDevices.size();i++)
    {
        ui->OutputTextBrowser->append(AvailableAudioInputDevices.at(i).deviceName());
    }
    /* Set up data format */
    DataFormat.setSampleSize(16);
    DataFormat.setSampleRate(16000);
    DataFormat.setCodec(QString("audio/pcm"));
    DataFormat.setSampleType(QAudioFormat::Float);
    DataFormat.setByteOrder(QAudioFormat::LittleEndian);
    DataFormat.setChannelCount(1);
    /* Check format supported */
    if(QAudioDeviceInfo::defaultInputDevice().isFormatSupported(DataFormat))
    {
        ui->OutputTextBrowser->append(QString::fromUtf8("Supported format."));
    }
    else
    {
        ui->OutputTextBrowser->append(QString::fromUtf8("Unsupported format."));
    }
    /* Open */
    Microphone=new QAudioInput(QAudioDeviceInfo::defaultInputDevice(), DataFormat);
    MicrophoneStream=Microphone->start();
}
MainWindow::~MainWindow()
{
    delete ui;
}

// ------------------------------------------

/* main.cpp */
#include "main_window.h"
#include <QApplication>
#include <QLocale>
#include <QTranslator>
int main(int argc, char *argv[])
{
    QApplication Application(argc, argv);
    QTranslator Translator;
    const QStringList UILanguages = QLocale::system().uiLanguages();
    for (const QString &locale : UILanguages)
    {
        const QString baseName = "Test1_QtWidgetApplication1_" + QLocale(locale).name();
        if (Translator.load(":/i18n/" + baseName))
        {
            Application.installTranslator(&Translator);
            break;
        }
    }
    MainWindow main_window;
    main_window.show();
    return Application.exec();
}

[SGaist]

Which version of Qt are you using ?

[asdlkjqpwoei]

@SGaist Qt 5.15.2

[asdlkjqpwoei]

This issue has been solved at c++ - QAudioInput: failed to open audio device.

Solution:
16bit audio must be signed integer.

DataFormat.setSampleType(QAudioFormat::SignedInt);