Novel Methods in H.264/AVC (Inter Prediction, Data Hiding, Bit Rate Transcoding)

H.264 Advanced Video Coding has become the dominant video coding standard in the market, within a few years after the first version of the standard was completed by the ISO/IEC MPEG and the ITU-T VCEG groups in May 2003. That happened mainly due to the great coding efficiency of H.264. Compared to MPEG-2, the previous dominant standard, the H.264 compression ratio is about twice as higher for the same video quality. That makes H.264 ideal for a numerous of applications, such as video broadcasting, video streaming and video conferencing. However, the H.264 efficiency is achieved at the expense of the codec?s complexity. H.264 complexity is about four times that of MPEG-2. As a consequence, many video coding issues, which have been addressed in previous standards, need to be re-considered. For example the H.264 encoding of a video in real time is now an open issue. Re-applying older solutions is feasible but insufficient because the new H.264 characteristics are not taken into account and thus the problems caused by these characteristics are not properly addressed. On the other hand, these characteristics make possible a series of applications that either were not possible or showed inferior results prior the H.264 era. This dissertation aims at investigating novel methods, which take advantage of the new characteristics introduced by H.264. These methods are of two categories, namely enhancements and applied methods. The goal of the enhancements is to improve the performance of the H.264 encoder by reducing its complexity. We focused on the inter prediction part of the encoder. Three representative methods of this category are introduced; a fast full search algorithm, which reduces the motion estimation time (53.7% a predictor, which optimizes the search area during the motion estimation and a reference frame selector, which reduces the motion estimation time (80%) by reducing the number of the reference frames during the motion estimation. The applied methods, on the other hand, exploit the special H.264 characteristics in order to improve their performance. Two data hiding methods are introduced, which result in high capacity of hidden data, e.g. 18 Kbits of data in 10 sec (30 fps) of video. In particular, the data hiding methods opened new directions in the research of the data hiding in video not only because of their unique capabilities (high data capacity, real time operation, reusability of the marked streams, etc.) but also because they moved the cost of the hidden data from the PSNR to the bit rate in contrast to all of the previously existing methods. In addition to the data hiding methods, a bit rate transcoder, which controls the bit rate directly in the compressed domain, is also introduced. Finally, a moving object detection method and a scene change detection method complete the repertoire of the applied methods.