QMediaRecorder::record() delay on Windows

SGaist

Hi,

Do you have the same issue if you run in release mode ? Debug mode can sometime incur performance hit that can explain such behaviour.

szumial

@SGaist In Release mode I can observe the delay when recording audio. In Debug mode I reached the exception posted in the original message.

SGaist

Do you have the same issue if you trigger the recoding using the button's clicked signal ?

szumial

@szumial Yes, it happens also when I trigger the recording using the "clicked" signal.

Whatever I do, there is always a noticeable delay. Before the recorder goes to RecordingState it is around 3 seconds when I trigger recording for the first time. Consecutive times have a slightly smaller delay time.

Here is a sample of my code:

// QMediaRecorder settings
m_recorder.setMediaFormat({QMediaFormat::MP3});
m_recorder.setAudioChannelCount(1);
m_recorder.setQuality(QMediaRecorder::Quality::VeryHighQuality);
m_recorder.setEncodingMode(QMediaRecorder::ConstantQualityEncoding);

// Pushbutton connections
connect(recordButton, &QToolButton::pressed, this, [this]
{
    record(true);
});
connect(recordButton, &QToolButton::released, this, [this]
{
    record(false);
});

// Record method
void MyWidget::record(bool on)
{
    if (on)
    {
        recordButton->setChecked(true);
	QDir{}.mkpath(m_outputPath); 
        m_recorder.setOutputLocation(QUrl::fromLocalFile(m_recordedFile));
	m_audio->recorder().record();
	recordButton->setText(tr(" Recording..."));
    }
    else
    {
        recordButton->setChecked(false);
        m_recorder.stop();
	recordButton->setText(tr(" Start recording"));
    }
}

SGaist

Might be a silly question but where are you starting the recording ? Is it locally ? On a network drive ?

szumial

@SGaist I am recording the microphone input to a local drive.

I was wondering if moving the recorder logic to a separate thread could improve it, but initial trials did not bring any benefits.

Another idea I have is a silly workaround to start recording at program start in order for any QMediaRecorder resources to be initialized before I trigger the recording with that pushbutton. This would not solve the root cause of the problem, but maybe improve user experience at least.

SGaist

Do you encounter the same issue if you use your application on a different machine ?

szumial

@SGaist Yes, that is on Windows PCs. I don't see such issue when running my program on MacOS.

SGaist

Just to be sure I understand this correctly, you have the same issue in several different Windows machines ?

szumial

@SGaist That is correct. The same application tested on different Windows machines presents exactly the same behavior.