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 data blocks of the received data stream until an occurrence of the data block modification period occurs; and modifying 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, and wherein the modifying the current data block corresponding to the occurrence of the data block modification period, comprises: if a ratio of the SPR to the NPR is greater than 1.0, cross-fading the current data block with a next data block in the data stream; and if a ratio of the SPR to the NPR is less than 1.0, then cross-fading the current data block with itself.