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.