Battery life in portable entertainment devices that play fixed-length music or video files (e.g., MP3 music files) is extended by adaptively adjusting the speed of a processor in the device such that only a minimum number of MIPS are performed to playback the music or video files. Slowing the processor clock provides significant savings in power usage. A use profile containing required MIPS for each song may be stored on the device, or use profile information may be inserted into the data stream or embedded within the data file. Power savings occurs on every subsequent replay of the same entertainment data file or data stream by adaptively adjusting the processor clock to the desired speed as determined by the use profile information (plus design margin based on the particular playback device).