vaapioverlay: add minimal documentation

gst-libs/gst/vaapi/gstvaapiblend.c

@@ -289,6 +289,19 @@ gst_vaapi_blend_process_unlocked (GstVaapiBlend * blend,
   return TRUE;
 }
 
+/**
+ * gst_vaapi_blend_process:
+ * @blend: a #GstVaapiBlend instance.
+ * @output: a #GstVaapiSurface to be composed.
+ * @next: a function to fetch the next #GstVaapiBlendSurface to
+ *    process.
+ * @data: state storage for @next.
+ *
+ * This function will process all the input surfaces defined through
+ * #GstVaapiBlendSurface and will blend them onto the @output surface.
+ *
+ * Returns: %TRUE if the blend process succeed; otherwise %FALSE.
+ **/
 gboolean
 gst_vaapi_blend_process (GstVaapiBlend * blend, GstVaapiSurface * output,
     GstVaapiBlendSurfaceNextFunc next, gpointer user_data)

gst/vaapi/gstvaapioverlay.c

@@ -20,6 +20,27 @@
  *  Boston, MA 02110-1301 USA
 */
 
+/**
+ * SECTION:element-vaapioverlay
+ * @title: vaapioverlay
+ * @short_description: a VA-API base video compositor
+ *
+ * The vaapioverlay element is similar to the base compositor element
+ * but uses VA-API VPP blend functions to accelerate the
+ * overlay/compositing.
+ *
+ * Currently this element only works with iHD driver.
+ *
+ * ## Example launch line
+ *
+ * |[
+ *   gst-launch-1.0 -vf videotestsrc ! vaapipostproc      \
+ *     ! tee name=testsrc ! queue                         \
+ *     ! vaapioverlay sink_1::xpos=300 sink_1::alpha=0.75 \
+ *     name=overlay ! vaapisink testsrc. ! queue ! overlay.
+ * ]|
+ */
+
 #include "gstvaapioverlay.h"
 #include "gstvaapipluginutil.h"
 #include "gstvaapivideobufferpool.h"