QAudioProbe::audioBufferProbed() behavior

[yodl]

I have a QMediaPlayer which I set as source for a QAudioProbe. Then I connect the signal audioBufferProbed() to a private slot in my class like this:

connect(m_probe, SIGNAL(audioBufferProbed(const QAudioBuffer&)), this, SLOT(processAudioProbe(const QAudioBuffer&)));

Here's what I don't understand: I have a button for opening an audio file and one for playing it. As soon as I open the file, audioBufferProbed() is emmitted, even before I even clicked play. What data do I get here? Why is the buffer probed before the player even plays?

Here's the open function:

void MainWidget::openFile(const QString &fileName)
{
    QUrl url = QUrl::fromLocalFile(fileName);
    QMediaContent media(url);
    m_player->setMedia(media); // this already seems to trigger audioBufferProbed()
}

Here's play:

void MainWidget::startPlayback()
{
    m_player->play();
}

[SGaist]

Hi and welcome to devnet,

Does it happen also when you open a file the first time ? Or only after you already opened one and replace it with another ?

[yodl]

Hi,

It happens also the first time I open a file.

[SGaist]

What version of Qt and OS are you using ?

[yodl]

I'm on Ubuntu 14.04 using Qt 5.5.1 64 bit.

[yodl]

I created a minimal working example which demonstrates the issue: https://bitbucket.org/rdssdf/mweaudioprobe

[SGaist]

Since you're on Linux, It might be something that's GStreamer specific.

[yodl]

Ok, I just confirmed that the issue does not occur on Windows. You are probably right that it is GStreamer specific. So... what are my options on Linux? Can I configure GStreamer somehow or can I run Qt with a different audio framework? I'd really like to build my app for Linux as well.

[SGaist]

Depending on your Qt version you could rebuild the multimedia module using GStreamer 1.0

[yodl]

I rebuilt Qt 5.5 from source with GStreamer 1.0 but it's still the same. Btw, is there a way to rebuild a module and pass configure options using the web installer? I had to checkout the sources from git and compile them because I could not find out how to do it.

[SGaist]

You can get the sources from the installer but not start a build from there.