From Hydrogenaudio Knowledgebase
Sac is an apparently experimental lossless audio codec. It comes with source code and a Windows 64-bit executable.
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Sac is arguably not an end-user codec, lacking pretty much all the features those possess (see the HA Wiki's Lossless Codec Comparison). Rather, it seems to be dedicated to achieving smaller file size than any other lossless codec whatever computing power it might take. Thus, decoding might fall severely short of real-time speeds: The developer uses as benchmark OptimFROG's max preset, which has been measured to decode at around 4x realtime; cursory testing indicates that Sac (v0.5.1) is order of magnitude ten times as CPU intensive. Independent comparison measured Sac does to smaller files size on average (but not all) material.