MediaPlayer {
        id: player
        objectName: "qmlPlayer"
        source: "qrc:/imgs/ebalo.mp4"

    }
       VideoOutput {
           id: output
           source: player
           x: 0
           y: 0
           anchors.fill : parent
           width: parent.width
           height: parent.height
}

And i'm cast this into QMediaPlayer in qt side:

    QQmlEngine * engin = QQmlEngine::contextForObject(this)->engine();
    QQmlApplicationEngine *engine = qobject_cast<QQmlApplicationEngine*>(engin);
    QObject *qmlMedia = engine->rootObjects().at(0)->findChild<QObject*>("qmlPlayer");
    player = qvariant_cast<QMediaPlayer *>(qmlMedia->property("mediaObject"));
    connect(&probe,&QVideoProbe::videoFrameProbed,this,&ClassBuilder::handleFrame);
    qDebug()<<probe.setSource(player)<<"player"<<player<<player->errorString();
    probe.setSource(player);

QDebug output is: false player QMediaPlayer(0xbe1ac010) ""
why is setSource returns false?
Replacing the MediaPlayer with the QCamera everything works as it should, maybe grabbing frames via QVideoProbe from QMediaPlayer is not supported on android?