The present default value of 0 will render the overlay video invisible.
A default of 1.0 is consistent with most common use cases.
Signed-off-by: Fei Wang <fei.w.wang@intel.com>
Reviewed-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>