Files with the HMT extension were used by a technology developed by Microsoft and Panasonic called HighMAT. HMT files were used to store all kinds of multimedia content (images, audio, video). These files were placed on CDs. This format could be supported by consumer electronics devices such as DVD players, CD players or car radios.

Microsoft has withdrawn from support for HighMAT technology, and the HMT format is now rarely used and considered obsolete.