Boot2Qt video dropping frames on RPI3 (even though gstreamer directly is working fine)

Hi.

Not sure about the right place to open this, but building Boot2Qt with Qt 5.9.4 or latest 5.10.1 from the poky branch results in a choppy video playback when using QML Video element or QVideoWidget on a RPI3.

using QML

Video
{     
    source: "test.mp4" // youtube-dl -f 137+140 https://www.youtube.com/watch?v=T63MCogI4sM
    autoPlay: true
    anchors.fill: parent
}

using QVideoWidget

    QMainWindow w;
    QMediaPlayer player;
    QVideoWidget videoWidget;

    w.setCentralWidget(videoWidget);

    player.setMedia(QUrl::fromLocalFile("/home/root/test.mp4"));
    player.setVolume(100);
    player.setVideoOutput(videoWidget);

    videoWidget.show();
    w.showFullScreen();

    player.play();
}

I've added gstreamer1.0-omx to the layer but video is still not smooth (dropped frames).
GST_DEBUG does show that omx is being used.
Playing video directly by using

gst-play-1.0 test.mp4

video is running as expected.
I've tried many different combinations in the past 4-5 days but I wasn't able to get this up and running on any distribution on the RPI device.
I found something along these lines but I'm not sure how relevant this is (since it was merged in gstreamer 1.8 and 1.10 is used by Boot2Qt that I'm testing with) https://bugzilla.gnome.org/show_bug.cgi?id=763044

I would expect this to just work in Boot2Qt, should it or what are the options?

EDIT: I've also compiled and tested yocto rocko with gstreamer 1.12 as I've seen some qmlglsrc improvements but no difference in the end.

Thanks,
Petar