I try to run a video using qtmultimedia 5.4.0 examples with built in support for gstreamer-1.0 on a board using wayland-egl with weston.
I get this error: "No m_videoSink available!"

So, after looking into the code -> file src/gsttools/qgstreamervideowidget.cpp, in method QGstreamerVideoWidgetControl::createVideoWidget(). It is creating X11 specific sink. I guess for wayland, "waylandsink" should be created. Maybe using some sink component like "autovideosink" if available?

m_videoSink = gst_element_factory_make ("xvimagesink", NULL);
m_videoSink = gst_element_factory_make ("ximagesink", NULL);

gst specific functions to manage the m_videoSink:

#if !GST_CHECK_VERSION(1,0,0)
if (m_videoSink && GST_IS_X_OVERLAY(m_videoSink))

{ gst_x_overlay_set_xwindow_id(GST_X_OVERLAY(m_videoSink), m_windowId); }

#else
if (m_videoSink && GST_IS_VIDEO_OVERLAY(m_videoSink))

{ gst_video_overlay_set_window_handle(GST_VIDEO_OVERLAY(m_videoSink), m_windowId); }

#endif

By the way, on last code, when using gst-0.10, according to ( http://www.freedesktop.org/software/gstreamer-sdk/data/docs/latest/gst-plugins-base-libs-0.10/gst-plugins-base-libs-gstxoverlay.html#gst-x-overlay-set-xwindow-id ):
"gst_x_overlay_set_xwindow_id is deprecated and should not be used in newly-written code. Use gst_x_overlay_set_window_handle() instead."

These links also confirmes lack of integration with wayland:
https://bugs.tizen.org/jira/si/jira.issueviews:issue-html/PTREL-792/PTREL-792.html
https://www.mail-archive.com/ivi@lists.tizen.org/msg02525.html

Also some related interesting links which might be of help to know more about the issue/solution:
https://gkiagia.wordpress.com/2014/06/10/gstreamer-on-wayland-with-gtk/
https://bugreports.qt.io/browse/QTBUG-29024