Optional allowedAllows configuring which mime types are allowed during ad playback.
 - This feature is only available for Google IMA.
 - If set to an array, all ads with another mime types will be ignored.
 - If set to undefined the ad system will pick media based on the browser's capabilities.
undefined
Optional googleThe Google IMA configuration.
Optional preloadWhether media files of mid- and postrolls are preloaded.
 - This feature is only available for Google IMA.
'midroll-and-postroll'
Optional showWhether an advertisement duration countdown will be shown in the UI.
use GoogleImaConfiguration.uiElements instead
 - Available since v2.22.9.
 - This feature is only available for Google IMA.
true
Optional vpaidThe iframe policy for VPAID ads.
 - This feature is only available for Google IMA and SpotX.
'enabled'
Describes the configuration of advertisement.