Provide a method to list the supported metadata apis.
Activate the video metadata on buffers when a downstream element configured the
bufferpool to support that api.
Use GstVideoInfo to keep track of the configured format.
Add GstMetaVideo to buffers, disabled by default for now until we can have it
enabled with a property on the bufferpool configuration.
Improve bufferpool handling in ximagesink.
Implement bufferpool handling on xvimagesink.
Based on patches from benjamin gaignard <benjamin.gaignard@linaro.org>