Clean public APIs up so that to better align with the decoder APIs.
Most importantly, gst_vaapi_encoder_get_buffer() is changed to only
return the VA coded buffer proxy. Also provide useful documentation
for the public APIs.
Fix the GstVaapiEncoderClass parent class type. Make sure to validate
subclass hooks as early as possible, i.e. in gst_vaapi_encoder_init(),
thus avoiding useless run-time checks. Also simplify the subclass
initialization process to be less error prone.
Refactor the GstVaapiCodedBuffer APIs so that to more clearly separate
public and private interfaces. Besides, the map/unmap APIs should not
be exposed as is but appropriate accessors should be provided instead.
* GstVaapiCodedBuffer: VA coded buffer abstraction
- gst_vaapi_coded_buffer_get_size(): get coded buffer size.
- gst_vaapi_coded_buffer_copy_into(): copy coded buffer into GstBuffer
* GstVaapiCodedBufferPool: pool of VA coded buffer objects
- gst_vaapi_coded_buffer_pool_new(): create a pool of coded buffers of
the specified max size, and bound to the supplied encoder
* GstVaapiCodedBufferProxy: pool-allocated VA coded buffer object proxy
- gst_vaapi_coded_buffer_proxy_new_from_pool(): create coded buf from pool
- gst_vaapi_coded_buffer_proxy_get_buffer(): get underlying coded buffer
- gst_vaapi_coded_buffer_proxy_get_buffer_size(): get coded buffer size
Rationale: more optimized transfer functions might be provided in the
future, thus rendering the map/unmap mechanism obsolete or sub-optimal.
https://bugzilla.gnome.org/show_bug.cgi?id=719775
