| As we all know, the video is intuitional and vivid for us to get the information.And with the rapid development of science and technology, the network infrastructures and computer peripheral products are more and more sophisticated, various digital imaging equipments are invented, video and audio processing hardware and related software technology continually innovate. Therefore, the video as a information carrier is widely used. But the digital video brings huge amount of information, by which people are puzzled.H.264is the new generation vide coding standard. It was jointly proposed by ISO and ITU. The H.264standard is currently one of the most commonly used formats for the recording, compression and distribution of high definition vdieo. Compared with peering video coding standards, H.264/AVC can in general achieve a higher compression ratio at the same restored video quality. Nevertheless, in the design and implementation of a concrete H.264/AVC video encoder, many considerations are required on its computaional effciency. For a typical H.264/AVC video encoder, its computaional complexity resides mainly in several components such as intra prediction,4×4block-based transformation and variable block size motion estimation. Among the various components, motion estimation and mode decision usually accounts for a very large portion of the video encoder’s computaion. As such, we focus on efficient motion estimation and mode decision for H.264/AVC video encoder in this work.Our main work are:1. Introduction to video coding standard.2. Introduction to motion estimation and mode decision. Analyse the classical motion estimaiton and mode decision algorithms.3. In this paper, we propose an efficient motion consistency based motion estimation algorithm for H.264/AVC. According to a proposed metric of motion consistency, each block is categorized as either a motion consistent block or a motion inconsistent block. Different motion estimation methods are employed for different types of blocks. For a motion consistent block, efficient diamond search or hexagon search is employed depending on the extent of motion activity contained in the local neighborhood; for a motion inconsistent block, we propose a dynamic hierarchical search method yielding a good tradeoff between efficiency and accuracy. For most of the test video sequences as used in our experiments, the proposed algorithm leads to a significant advantage in computational efficiency at only slight increase in coding bitrate and/or slight decrease in peak signal-to-noise ratio, when compared with a set of peering algorithms.4. In this paper, we propose a fast mode decision algorithm for H.264/AVC. It is based on the spatio-temporal coherency of the local neighborhood including and around the current block. We first build the histograms of the current block and the co-located block in the reference frame, respectively. If the difference between the two histograms is small, we use large-block-size modes. Otherwise, we subdivide the current block into four equal-sized sub-blocks and estimate the motion vector (MV) for each. In general, if there is a high degree of coherency between those MVs, we use large-block-size modes and otherwise small-block-size modes. In addition, we use the number of neighboring large blocks and the sub-blocks’ rate-distortion (R-D)costs as further hints for the mode decision. As experimentally demonstrated, our algorithm leads to significant saving in computing time and coding bits on the test video sequences. |
PDF Full Text Request