An ad-marketplace system manages an exchange for advertisement opportunities from a plurality of content brokers. Each advertising opportunity can include one or more attributes that describe advertisement slots during a broadcast of a data stream. The ad-marketplace system can receive one or more bids for an advertising opportunity associated with a media stream, and can select a matching bid from an advertiser for the advertising opportunity. Each bid can specify one or more advertising requirements that are to be satisfied by the advertising opportunity. When the ad-marketplace system selects the matching bid, the ad-marketplace system establishes a contract between the media broker, and places an initial payment from the advertiser in escrow. The ad-marketplace system can provide a payment to the media broker after confirming that a set of consumers have consumed the advertisement.