Help with QThread

[ziggx]

Hi There,

I have a VideoPlayer and I want to put it into a separate thread, but I'm not sure how to do this. Here's my (shortened) code`

VideoPlayer :: VideoPlayer(QWidget *parent)
    :QGraphicsScene(parent)
    ,mediaPlayer(0,QMediaPlayer::VideoSurface)
    ,videoItem(0)
{
    videoItem=new VideoItem;
    mediaPlayer.setVideoOutput(videoItem);
    addItem(videoItem);
}

And here's the code for the VideoItem:

VideoItem::VideoItem(QGraphicsItem *parent)
    : QGraphicsItem(parent)
    , imageFormat(QImage::Format_Invalid)
    , framePainted(false)
{

}

VideoItem::~VideoItem()
{
}

QRectF VideoItem::boundingRect() const
{    
    return QRectF(QPointF(0,0), surfaceFormat().sizeHint());
}

void VideoItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    Q_UNUSED(option);
    Q_UNUSED(widget);

    if (currentFrame.map(QAbstractVideoBuffer::ReadOnly)) {
        const QTransform oldTransform = painter->transform();

        if (surfaceFormat().scanLineDirection() == QVideoSurfaceFormat::BottomToTop) {
           painter->scale(1, -1);
           painter->translate(0, -boundingRect().height());
        }

        painter->drawImage(boundingRect(), QImage(
                currentFrame.bits(),
                imageSize.width(),
                imageSize.height(),
                imageFormat));

        painter->setTransform(oldTransform);

        framePainted = true;

        currentFrame.unmap();
    }
}

QList<QVideoFrame::PixelFormat> VideoItem::supportedPixelFormats(
        QAbstractVideoBuffer::HandleType handleType) const
{
    if (handleType == QAbstractVideoBuffer::NoHandle) {
        return QList<QVideoFrame::PixelFormat>()
                << QVideoFrame::Format_RGB32
                << QVideoFrame::Format_ARGB32
                << QVideoFrame::Format_ARGB32_Premultiplied
                << QVideoFrame::Format_RGB565
                << QVideoFrame::Format_RGB555;
    } else {
        return QList<QVideoFrame::PixelFormat>();
    }
}

bool VideoItem::start(const QVideoSurfaceFormat &format)
{
    if (isFormatSupported(format)) {
        imageFormat = QVideoFrame::imageFormatFromPixelFormat(format.pixelFormat());
        imageSize = format.frameSize();
        framePainted = true;

        QAbstractVideoSurface::start(format);

        prepareGeometryChange();
        emit sizeChanged(boundingRect());
        return true;
    } else {
        return false;
    }
}

void VideoItem::stop()
{
    currentFrame = QVideoFrame();
    framePainted = false;

    QAbstractVideoSurface::stop();
}

bool VideoItem::present(const QVideoFrame &frame)
{
    if (!framePainted) {
        if (!QAbstractVideoSurface::isActive())
            setError(StoppedError);

        return false;
    } else {
        currentFrame = frame;
        framePainted = false;
        update();
        emit frameChanged();
        return true;
    }
}

I think I need to put the VideoItem's present function into a QThread but I am not sure how to do it. So my question is: is it the right place to use QThread and if so how do I go about it? Any help or suggestions would be gratefully received.

Thanks in advance
Best wishes
Ziggx

[mrjj]

Hi
You cannot have any widgets (GUI) in another thread. That is not allowed at all.
All GUI must stay in main thread.
But why you want to run player in a thread ?

[ziggx]

The app is a bit sluggish when running video - I use videoitem to emit a signal whenever there is a new frame (I need this to update timecode). I had hoped that using Thread would let it run faster. But from what you say, I simply can't do that.

Hmm... I'll have to think again.

Thanks for your reply

Best wishes
Ziggx

[jsulm]

@ziggx said in Help with QThread:

I need this to update timecode

How heavy is this updating?

[ziggx]

It needs to run on every new frame. :(

[jsulm]

@ziggx It's not what I asked. The question is: how long does each calculation for this update take?

[ziggx]

Hmm... checked the elapsed time for that function and it is 1ms or less. The problem is obviously somewhere else. I'm on OSX and the activity monitor shows I have lots of idle wakeups - could the OS be slowing things down?

Best wishes
Ziggx