Add a "vaapidecodebin" element to vaapi plugins.
Child Elements: "vaapidecode ! queue ! vaapipostproc"
The Reasons for implementing a new bin element:
-- Help to Autoplug Hardware Accelerated Video Postprocessing element in playbin
with out any dependency to upstream gstreamer.
This is to overcome the *unacceptable* delay in upstream gstreamer to get new
features in. Eg: https://bugzilla.gnome.org/show_bug.cgi?id=687182.
Also customers using older gstreamer versions (1.2 and 1.4) will get the
benefit of autoplugging, hardware accelerated deinterlacing support etc.
-- Help to maintain a single thread implementation in vaapidecode.
This will result a dead-lock free vaapidecode in most of the cases.
More details here: https://bugzilla.gnome.org/show_bug.cgi?id=742605https://bugzilla.gnome.org/show_bug.cgi?id=745216
