If the event is in reply to a request (made with this API and this
API handle), this is set to the reply_userdata parameter of the request
call. Otherwise, this field is 0.
Used for:
MPV_EVENT_GET_PROPERTY_REPLY
MPV_EVENT_SET_PROPERTY_REPLY
MPV_EVENT_COMMAND_REPLY
MPV_EVENT_PROPERTY_CHANGE
MPV_EVENT_HOOK
If the event is in reply to a request (made with this API and this API handle), this is set to the reply_userdata parameter of the request call. Otherwise, this field is 0. Used for: MPV_EVENT_GET_PROPERTY_REPLY MPV_EVENT_SET_PROPERTY_REPLY MPV_EVENT_COMMAND_REPLY MPV_EVENT_PROPERTY_CHANGE MPV_EVENT_HOOK