{Audio,Video}CapsBuilder: add for_encoding constructors
{Audio,Video}CapsBuilder
s provide new
and default
constructors, both of which build internal gst::caps::Builder
with encodings ".../x-raw".
This MR adds new for_encoding
constructors so that we can benefit from the {Audio,Video}CapsBuilder
API for other encoded formats.
Fixes #444 (closed)