Connect QAudioProbe to QMediaPlayer with RaspberryPi0

[davidino]

Goodmorning,
I'm using an image made with boot2qt version QT 5.12.0
As shown in the code below I'm trying to get the audio level out of a mediaPlayer made in QML. I can correctly setSource to the mediaplayer but the slot processBuffer is never called.
For information the audio is played via HDMI.
Can you advice?

#include <QObject>
#include <QAudioProbe>
#include <QMediaPlayer>
#include <QTimer>
#include <vector>
#include <memory>

#include "playListModel_global.h"

class PLAYLISTMODEL_EXPORT VolumeLevel : public QObject
{
    Q_OBJECT
public:
    VolumeLevel(QObject *parent = nullptr);
    ~VolumeLevel();

    Q_INVOKABLE void initVolume(QString qmlObjectName);
    void initVolume(QMediaPlayer *player);

public slots:
    void processBuffer(QAudioBuffer buffer);
    void timerExpired();

private:
    QAudioProbe probe;
    QTimer timer;
    QMediaPlayer *player;
};

#endif // VOLUMELEVEL_H




#include "volumelevel.h"
#include <QDebug>

#include <QAudioProbe>

VolumeLevel::VolumeLevel(QObject *parent) :
    QObject(parent)
{}

void VolumeLevel::initVolume(QString qmlObjectName)
{
    player = static_cast<QMediaPlayer*>(QObject::findChild<QObject*>(qmlObjectName));
    initVolume(player);
}

void VolumeLevel::initVolume(QMediaPlayer* player)
{
    if(probe.setSource(player)) {
        connect(&probe, &QAudioProbe::audioBufferProbed, this, &VolumeLevel::processBuffer);
        connect(&timer, &QTimer::timeout, this, &VolumeLevel::timerExpired);
        qDebug()<<"Connection done";
        timer.start(1000);
    }
}

void VolumeLevel::processBuffer(QAudioBuffer buffer)
{
    // With a 16bit sample buffer:
    const quint16 *data = buffer.constData<quint16>();
    qDebug()<<"Raw: "<<*data;
}

void VolumeLevel::timerExpired()
{
    qDebug()<<"probe is active: "<<probe.isActive();
}

VolumeLevel::~VolumeLevel()
{

}

[davidino]

Here, you can find the solution.
https://forum.qt.io/topic/115268/cast-a-qobject-to-qmediaplayer-with-qobject_cast

Regards,
Davidino

[jsulm]

@davidino said in Connect QAudioProbe to QMediaPlayer with RaspberryPi0:

player = static_cast<QMediaPlayer*>(QObject::findChild<QObject*>(qmlObjectName));

Did you check whether player is not nullptr?

[davidino]

Hello @jsulm,
you are right. I've modified the function as follow:

void VolumeLevel::initVolume(QString qmlObjectName)
{
    player = QObject::findChild<QMediaPlayer*>(qmlObjectName);
    if(player != nullptr)
        initVolume(player);
    else
        qDebug()<<"MediaPlayer not found "<<qmlObjectName;
}

Unfortunately I still get object not found. In QML the MediaPlayer is defined as follow:

    MediaPlayer {
        id: playMusic
        objectName: "mediaplayer"
        autoLoad: true
        autoPlay: true
        playlist: Playlist{id:playerList}
        property Volume volumeMeter : Volume {id: volume}
        Component.onCompleted: volume.initVolume(playMusic.objectName)
    }

I've register Volume in main.cpp as:
qmlRegisterType<VolumeLevel>("VolumeLib", 1, 0, "Volume");

[jsulm]

@davidino said in Connect QAudioProbe to QMediaPlayer with RaspberryPi0:

QObject::findChild<QMediaPlayer*>(qmlObjectName);

findChild() is not static! It finds children of a parent. You need to call findChild on the widget which is parent of your QML object.

[davidino]

Hello @jsulm ,
you are right, I didn't read carefully the documentation. I tried several attempts and still I cannot figure it out. This is my last changing:

void VolumeLevel::initVolume(QString qmlObjectName)
{
    if(parent() != nullptr) 
    {
        qDebug()<<"Parent name is: "<<parent()->objectName();
        player = parent()->findChild<QMediaPlayer*>(qmlObjectName);
        if(player != nullptr)
            initVolume(player);
        else
            qDebug()<<"MediaPlayer not found "<<qmlObjectName;
    }
}

    Item {
        id: musicSystem
        objectName: "musicSystem"

        MediaPlayer {
            id: playMusic
            objectName: "mediaSystem"
            autoLoad: true
            autoPlay: true
            playlist: Playlist{id:playerList}
        }
        Volume {id:volume; objectName: "volumeSystem"}

        Component.onCompleted: volume.initVolume(playMusic.objectName)
    }

The result is the following, it can identify correctly musicSystem as the parent but not the mediaplayer
Parent name is: "musicSystem"
MediaPlayer not found "mediaSystem"

I tried also with the approach:
QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:/music/MusicPage.qml")));
QObject *object = component.create();
but with no success.

Thank you.
Regards,
Davide

[davidino]

Here, you can find the solution.
https://forum.qt.io/topic/115268/cast-a-qobject-to-qmediaplayer-with-qobject_cast

Regards,
Davidino