Introducing differential motion estimation into hybrid video coders Differential motion estimation produces dense motion vector fields which are far too demanding in terms of coding rate in order to be used in video coding. However, a pelrecursive technique like that introduced by Cafforio and Rocca can be modified in order to work using only the information available at the decoder side. This allows to improve the motion vectors produced in the classical predictive modes of H.264. In this paper we describe the modification needed in order to introduce a differential motion estimation method into the H.264 codec. Experimental results will validate a coding mode, opening new perspectives in using differentialbased motion estimation techniques into classical hybrid codecs.

Advances in hybrid video coding Hybrid video coding is known for a long time and is applied in all video coding standards such as MPEGx or H.26x. This paper shows that there is still enough potential for further coding efficiency improvements. The paper starts with an overview of stateoftheart hybrid video coding schemes such as H.264AVC. Thereafter, our advances on main building blocks of H.264AVC are presented that significantly improve the coding efficiency. For instance, intra prediction is improved by changing scan directions and thus providing better reference pixels for specific prediction directions. Adaptive filtering and high precision motion compensation improves the motion compensated prediction. Furthermore, the combination of transformation, quantization, and entropy coding of the prediction error is improved using an advanced frequency selective coding technique. With the transmission of postfilter hints it is possible to design a Wiener postfilter that significantly enhances the picture quality. Finally, texture synthesis techniques are used to improve the subjective quality for specific textures with homogenous statistical characteristics. This paper presents our abovementioned techniques in detail. Depending on the input sequence and the bit rate, the objective andor subjective gains compared to H.264AVC are quite significant.