The sum of absolute transformed differences (SATD) is a block matching criterion widely used in fractional motion estimation for video compression.
SATD is slower than the sum of absolute differences (SAD), both due to its increased complexity and the fact that SAD-specific MMX and SSE2 instructions exist, while there are no such instructions for SATD.
However, SATD can still be optimized considerably with SIMD instructions on most modern CPUs.
The benefit of SATD is that it more accurately models the number of bits required to transmit the residual error signal.
As such, it is often used in video compressors, either as a way to drive and estimate rate explicitly, such as in the Theora encoder (since 1.1 alpha2),[1] as an optional metric used in wide motion searches, such as in the Microsoft VC-1 encoder, or as a metric used in sub-pixel refinement, such as in x264.