"Run-Level" coding refers to coding a run-length of zeros followed by a nonzero level.  Instead of sending all the zero values individually, the length of the run is sent.  This technique was first used prominently in facsimile transmission of two-level images of text documents, but is useful for any data with long runs of zeros.  Run lengths are easily encoded by a Huffman code.  Refer to Huffman/Run-Level Coding for discussion of application to MPEG.

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