Qt5 QWebView HTML5 video tag support

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C++

QT

HTML5

QT-Creator

Hi All,
I am trying to play .mp4 file in QWebView of Qt using HTML5 video support(I can not use any plugin or adobe flash).
I have 3 system. newly installed Windows 7 x64, Mac OS X 10.7 and Windows xp X64.
I get new Qt 5.0 for windows and Mac and installed on all systems. I have also installed full VLC (for codec) on all 3 system. Then i create a Qt program as below.

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWebView view;
    QWebSettings::globalSettings()->setAttribute(QWebSettings::PluginsEnabled, true);
    view.settings()->setAttribute(QWebSettings::PluginsEnabled, true);
    QUrl url("http://www.html5test.com"); // html5test.com is site to check which features of html5 your browser supports.
    view.load(url);
    view.show();
    return a.exec();
}

What i see is On windows 7 and Mac OS X gives that video and audio tag supported, and also MP4 video format supported on both os. But it shows 0 rating on windows xp x64 for video tag support. I google for this but could not get anything helpful. Why it says that video and audio tag not supported on Windows xp X64?

After that i try to load a website having different videos with

<video>

tag as below.

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    QWebView view;
    QWebSettings::globalSettings()->setAttribute(QWebSettings::PluginsEnabled, true);
    view.settings()->setAttribute(QWebSettings::PluginsEnabled, true);
    QUrl url("http://shapeshed.com/examples/HTML5-video-element/");// having video tags
    view.load(url);
    view.show();
    return a.exec();
}

When i run above code, On Mac it run as per required. On windows 7 It shows the video controls (Play button, seek bar ) but it could not play video. And on Windows xp X64 machine no video and video control visible.
Whats Wrong with windows 7 machine if it says that video tag and mp4( and H.264) is supported?
I have other browsers too on all system where all above works nicely.
Is there any system specific settings required? or did I miss any important step(s)?
Thanks all.