MPEG Surround
MPEG Surround (ISO/IEC 23003-1 or MPEG-D Part 1), also known as Spatial Audio Coding (SAC), is a lossy compression format for surround sound that provides a method for extending mono or stereo audio services to multi-channel audio in a backwards compatible fashion. The total bit rates used for the (mono or stereo) core and the MPEG Surround data are typically only slightly higher than the bit rates used for coding of the (mono or stereo) core.