This prevents the ugly hack where the text_sink pad template
was only added for textoverlay but not for the subclasses.
Also makes this work with the core change that made
subclasses inherit the templates of their parent class.
The textoverlay element will rerender the text string whenever
overlay sets the 'need_render' flag to TRUE. Previously, we
lazily set the flag to TRUE every time the time string was requested.
Now, we save a copy of the previously given string, and only set
'need_render' to TRUE if the string has changed.
In my tests with a 30fps video stream, and a time string including
a seconds field, this change reduced the CPU usage of the clockoverlay
element from 60% to 5%.
Fixes bug #627780.
And fix the resulting compile failures.
I'm sorry about the patch necessary to gstclockoverlay.h but after
talking to Tim we decided we can live with it.
Original commit message from CVS:
Patch by: Pavel Zeldin <pzeldin at gmail dot com>
* ext/pango/gstclockoverlay.c: (gst_clock_overlay_render_time),
(gst_clock_overlay_class_init), (gst_clock_overlay_finalize),
(gst_clock_overlay_init), (gst_clock_overlay_set_property),
(gst_clock_overlay_get_property):
* ext/pango/gstclockoverlay.h:
API: Add ability to specify format for date/time display by
adding a "time-format" property.
Fixes bug #554879.
