1. A computing resource efficient method for playing back a data stream formed of data blocks at a selected playback rate SPR, the method comprising: determining a minimum frequency of data blocks for modification to achieve the selected playback rate SPR; computing a data block modification period based upon the minimum frequency; receiving the data stream; passing through the data block of the received data stream until the occurrence of the data block modification period occurs; and modifying only a current data block corresponding to the occurrence of the data block modification period, wherein the selected playback rate SPR is no more than twice a normal playback rate NPR.