Method and apparatus for negotiation of streaming data, suitable for application in an environment wherein a server generates and serves large, continuous amounts of speech data to a client in real time. A method of controlling the play out of a generated data stream from a data stream player includes estimating a time for generating the data stream; estimating a time for playing the data stream; generating a data stream using a data stream generation resource, for output by the data stream player; and alerting the stream player if the remaining generation time is less than the play time. The server may calculate what it can do, given knowledge of the network, and send a message to guarantee a level of service. A “can start play” message may be sent to client when the client can reliably start playing the signal.