In a multimedia presentation transmitted by streaming media, advertising/announcements are dynamically inserted into the stream in response to a realization of conditions preselected by the source of the advertising/announcements. In a particular embodiment providers of the streaming media content define metadata for the programming. Advertising/announcement sources define metadata for their ads to be presented. The requirements of both metadata files are compared to both program data and ad data to specify conditions that determine when an Advertisement/announcement is inserted into a media stream.