  Efficient low-delay video encoders are of fundamental importance to provide
timely feedback in remotely controlled platforms such as drones. In order to
fully understand the theoretical limits of low-delay video encoders, we
consider an ideal differential predictive coded modulation (DPCM) encoder and
provide the explicit derivation of the sum-rate-distortion region for a generic
number of successive correlated Gauss-Markov sources along the line of the work
by Ma and Ishwar. Furthermore, we provide an upper bound on the minimum
distortion achievable in case an arbitrary number of sources are not available
at the decoder.
