• I am working on Windows.
• ffmpeg is on my path.
• ffmpeg works in command line.
• I tried giving the absolute path of ffmpeg to QProcess, no use.
• QtCreator version 17, with Qt 6.

The code I am running is below. Basically, when user clicks "convert" button, the app should start ffmpeg with QProcess. To be simple, I tried to get only version information with ffmpeg.

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QProcess *ffmpegProcess = new QProcess(this);
    ffmpegProcess->setWorkingDirectory(QCoreApplication::applicationDirPath());
    ffmpegProcess->setProcessChannelMode(QProcess::MergedChannels);
    
    // Connect buttons
    connect(ui->btnSelFile, &QPushButton::clicked, this, &MainWindow::selectInputFile);
    connect(ui->btnConvert, &QPushButton::clicked, this, &MainWindow::startConversion);

    // Connect FFmpeg process signals
    connect(ffmpegProcess, &QProcess::readyReadStandardOutput, this, &MainWindow::readProcessOutput);
    connect(ffmpegProcess, &QProcess::readyReadStandardError, this, &MainWindow::readProcessOutput);
    connect(ffmpegProcess, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
            this, &MainWindow::processFinished);
}

void MainWindow::selectInputFile()
{
    QString filePath = QFileDialog::getOpenFileName(this, "Select Video File", "", "Videos (*.mp4 *.mkv *.avi)");
    if (!filePath.isEmpty()) {
        inputFilePath = filePath;
        ui->txtLog->append("Selected file: " + filePath);
    }
}

void MainWindow::startConversion()
{
    QString ffmpegPath = "ffmpeg";
    QStringList args;
    args << "-version";
    ui->txtLog->append("Trying to run: " + ffmpegPath + " " + args.join(" "));
    ffmpegProcess->start(ffmpegPath, args);

    }
}

void MainWindow::readProcessOutput()
{
    QByteArray output = ffmpegProcess->readAllStandardOutput();
    QByteArray errorOutput = ffmpegProcess->readAllStandardError();

    if (!output.isEmpty()) {
        ui->txtLog->append(QString::fromLocal8Bit(output));
    }
    if (!errorOutput.isEmpty()) {
        ui->txtLog->append(QString::fromLocal8Bit(errorOutput));
    }
}


void MainWindow::processFinished(int exitCode, QProcess::ExitStatus status)
{
    Q_UNUSED(status);
    if (exitCode == 0) {
        ui->txtLog->append("✅ Conversion finished successfully!");
    } else {
        ui->txtLog->append("❌ Conversion failed.");
    }
}