The documentation of QMediaPlayerControl::availablePlaybackRanges () says :

"Usually for local files this is a continuous interval equal to [0..duration()] or an empty time range if seeking is not supported, but for network sources it refers to the buffered parts of the media."

The last part is completely wrong. At least looking at the QT7 and GStreamer backend there is no such code :

QMediaTimeRange QT7PlayerControl::availablePlaybackRanges() const
{
QMediaTimeRange result;

if (isSeekable())
result.addInterval(0, duration());

return result;
}

And the GStreamer backend has the same implementation.

Can be reproduced building webkit trunk, running QtTestBrowser and playing a video on tiny.cc/wkmedia, the timeline shows the video is completely buffered which is wrong.