Retrieving video size using QtGStreamer returns ZERO

I'm playing with QtGStreamer 0.10.0 and I'm trying to retrieve the video size but it's returning ZERO for height and width values.

However, I am able to play the video with no problems on a QImage.

QGst::init();        

pipeline = QGst::Pipeline::create();
filesrc = QGst::ElementFactory::make("filesrc");
filesrc->setProperty("location", "sample.avi");
pipeline->add(filesrc);

decodebin = QGst::ElementFactory::make("decodebin2").dynamicCast<QGst::Bin>();
pipeline->add(decodebin);
QGlib::connect(decodebin, "pad-added", this, &MyMultimedia::onNewDecodedPad);
QGlib::connect(decodebin, "pad-removed", this, &MyMultimedia::onRemoveDecodedPad);
filesrc->link(decodebin);

// more code ...

The code above shows the begining of the pipeline setup. By connecting my method MyMultimedia::onNewDecodedPad on the signal "pad-added" I have access to the data of the video. At least that's what I think.

void MyMultimedia::onNewDecodedPad(QGst::PadPtr pad)
{  
    QGst::CapsPtr caps = pad->caps();
    QGst::StructurePtr structure = caps->internalStructure(0);
    if (structure->name().contains("video/x-raw"))
    {
        // Trying to print width and height using a couple of different ways,
        // but all of them returns 0 for width/height.

        qDebug() << "#1 Size: " << structure->value("width").get<int>() << "x" << structure->value("height").get<int>();

        qDebug() << "#2 Size: " << structure->value("width").toInt() << "x" << structure->value("height").toInt();

        qDebug() << "#3 Size: " << structure.data()->value("width").get<int>() << "x" << structure.data()->value("height").get<int>();

        // numberOfFields also returns 0, which is very wierd.
        qDebug() << "numberOfFields:" << structure->numberOfFields(); 

    }

    // some other code
}

I wonder what I might be doing wrong. Any tips? I was unable to find a relevant example on the web using this API.

Solution

Solved it. At onNewDecodedPad() you still don't have access to information about the video frames.

The class MyMultimedia inherits from QGst::Utils::ApplicationSink, so I had to implement a method named QGst::FlowReturn MyMultimedia::newBuffer() that is called by QtGstreamer whenever a new frame is ready.

In other words, use this method to copy the frame of the video to a QImage. What I didn't know is that pullBuffer() returns a QGst::BufferPtr, which has a QGst::CapsPtr. It's an internal structure from this var that holds the information I was looking for:

QGst::FlowReturn MyMultimedia::newBuffer()
{
    QGst::BufferPtr buf_ptr = pullBuffer();        
    QGst::CapsPtr caps_ptr = buf_ptr->caps();
    QGst::StructurePtr struct_ptr = caps_ptr->internalStructure(0);

    qDebug() << struct_ptr->value("width").get<int>() << 
                "x" << 
                struct_ptr->value("height").get<int>();

    // ...
}