nested dpd

$meta_query = array(
	'relation' => 'AND',
	array(
		'key'     => 'highlight',
	),
	array(
		'relation' => 'OR',
		array(
			'key'     => 'post_type',
			'value'   => 'video',
		),
		array(
			'key'     => 'post_type',
			'value'   => 'image',
		),
	),
);