Optional.
Subclasses can override this to do their own
allocation of output buffers. Elements that only do
analysis can return a subbuffer or even just
return a reference to the input buffer (if in
passthrough mode). The default implementation will
use the negotiated allocator or bufferpool and
transform_size to allocate an output buffer or it
will return the input buffer in passthrough mode.
Optional. Subclasses can override this to do their own allocation of output buffers. Elements that only do analysis can return a subbuffer or even just return a reference to the input buffer (if in passthrough mode). The default implementation will use the negotiated allocator or bufferpool and transform_size to allocate an output buffer or it will return the input buffer in passthrough mode.