Data packets to be transferred over a network as part of a temporally ordered content stream are obtained by an adaptive progressive download (APD) server. The APD server divides the data packets of the content stream into epochs of contiguous data, the epochs including a current epoch. The APD server determines a bit rate available on the network for transferring the current epoch and calculates an estimate of a playback time of the content stream buffered at a computer to which the content stream is being transferred and played back. The calculation of the estimate is based at least in part on the bit rate available on the network and an encoding bit rate of the content stream. The APD server controls the transfer of the content stream over the network in accordance with the estimated playback time.