We consider the problem of streaming packetized media over the Internet from a server through a base station to a wireless client, in a rate-distortion optimized way. For error control, we employ an incremental redundancy scheme, in which the server can incrementally transmit parity packets in response to negative acknowledgements fed back from the client. Computing the optimal transmission policy for the server involves estimation of the probability that a single packet will be communicated in error as a function of the expected redundancy (or cost) used to communicate the packet. In this paper, we show how to compute this error-cost function, and thereby optimize the server's transmission policy, in this scenario.