Adaptive differential pulse-code modulation (ADPCM) is a variant of differential pulse-code modulation (DPCM) that varies the size of the quantization step, to allow further reduction of the required data bandwidth for a given signal-to-noise ratio.
Typically, the adaptation to signal statistics in ADPCM consists simply of an adaptive scale factor before quantizing the difference in the DPCM encoder.
ADPCM was developed in the early 1970s at Bell Labs for voice coding, by P. Cummiskey, N. S. Jayant and James L. Flanagan.
The Windows Sound System supported ADPCM in .wav files. The corresponding FFmpeg audio codecs are adpcm_ima_qt, adpcm_ima_wav, adpcm_ms, adpcm_swf and adpcm_yamaha.