Decoder-side block motion estimation for H.264 / MPEG-4 AVC based video coding

In video coding standards like H.264 / MPEG-4 AVC, the encoder performs motion estimation in order to utilise temporal dependencies within a sequence. In addition to the rate of the residue, the encoder has to allocate bits for motion vectors required to compensate the motion at the decoder. This bit rate increases for smaller block sizes, since more motion vectors need to be transmitted. Therefore, motion compensation using dense motion vector field is not feasible for such an architecture. This paper proposes to estimate motion for coding of B frames at the decoder. Using this decoder-side motion estimation, the transmission of the motion vectors is not necessary and the bit rate is reduced. Furthermore, prediction quality is higher in many cases resulting in a coding gain of up to 1.7 dB at low bit rates and 0.2 dB at higher bit rates.