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