IMA 4:1

A 4-to-1 cross-platform ADPCM codec built into QuickTime since 2.1.

Pro Audio Converter can convert audio files to and from IMA 4:1 via Core Audio.

IMA (Interactive Multimedia Association) 4:1 is a cross-platform audio codec which offers 4:1 compression and is built into QuickTime 2.1 and later. It only works on 16-bit audio and provides acceptable sound quality for the compression ratio.