refs:
https://bugzilla.gnome.org/show_bug.cgi?id=665080 
https://bugzilla.gnome.org/show_bug.cgi?id=658609
https://bugzilla.gnome.org/show_bug.cgi?id=685282

there is GstVideoOverlayComposition for a while, and i'm actually successfully using it. for that i've patched the pad templates of basetextoverlay and assrender so that they actually link into a pipeline with a sink that handles non-raw video with overlayed meta.

http://git.opendreambox.org/?p=opendreambox.git;a=blob;f=meta-opendreambox/recipes-multimedia/gstreamer/gstreamer1.0-plugins-bad/assrender-overlay-caps.patch;h=dddca2b2f0be1b030f7d8f98e30e80852ce96cb1;hb=9cec3d3682a75ab3e23d8a0784e65d73105e4843

http://git.opendreambox.org/?p=opendreambox.git;a=blob;f=meta-opendreambox/recipes-multimedia/gstreamer/gstreamer1.0-plugins-base/gstbasetextoverlay-overlaycaps.patch;h=790b722a6ecc246dab0f3d0fe787b29fd0ee56c5;hb=9cec3d3682a75ab3e23d8a0784e65d73105e4843

my q&d patches however seem to cause wild criticals somewhere deep inside:
(gst-play-1.0:499): GStreamer-CRITICAL **: gst_mini_object_ref: assertion `mini_object != NULL' failed

(gst-play-1.0:499): GStreamer-CRITICAL **: gst_caps_merge: assertion `GST_IS_CAPS (caps2)' failed

(gst-play-1.0:499): GStreamer-CRITICAL **: gst_mini_object_ref: assertion `mini_object != NULL' failed

(gst-play-1.0:499): GStreamer-CRITICAL **: gst_caps_merge: assertion `GST_IS_CAPS (caps2)' failed

(gst-play-1.0:499): GStreamer-CRITICAL **: gst_mini_object_ref: assertion `mini_object != NULL' failed

(gst-play-1.0:499): GStreamer-CRITICAL **: gst_caps_merge: assertion `GST_IS_CAPS (caps2)' failed

nevertheless, the overlays are correctly renderes and can be accessed and proprietarily blitted by our sink.

something is still missing, and the subtitle elements should eventually get a proper implementation for non-raw video streams.