Structure Theorems for Real-Time Variable-Rate Coding With and Without   Side Information
  The output of a discrete Markov source is to be encoded instantaneously by a variable-rate encoder and decoded by a finite-state decoder. Our performance measure is a linear combination of the distortion and the instantaneous rate. Structure theorems, pertaining to the encoder and next-state functions are derived for every given finite-state decoder, which can have access to side information. 
Yonatan Kaspi and Neri Merhav
cs.IT math.IT