QtQuick VideoOutput ignores the video format's viewport

When sending video frames into a VideoOutput item via QAbstractVideoSurface, you can specify a viewport in the format. VideoOutput seems to ignore it.

There's a comment in qdeclarativevideooutput.cpp (inside QDeclarativeVideoOutput::sourceRect()), which I'm assuming is relevant:

return QRectF(QPointF(), size); // XXX ignores viewport