将源设置为null一次后，Qml VideoOutput无法正常工作

Question

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtMultimedia 5.8

ApplicationWindow {
    visible: true
    width: 640
    height: 480

    property bool flip: true

    Timer {
        interval: 5000
        running: true
        repeat: true
        onTriggered: {
            flip = !flip
            if(flip) {
                videoOutput.source = null
            } else {
                videoOutput.source = player
            }
        }
    }

    VideoOutput {
        id: videoOutput
        anchors.fill: parent
        source: player
    }

    MediaPlayer {
        id: player
        source: "file://video.mp4"
        autoPlay: true
        loops:  MediaPlayer.Infinite
    }
}

在将Timer设置为videoOutput.source的{​​{1}}触发后，它将再次无效。 null只会对先前解码过的帧进行过时的绘制，并且永远不会改变。