最佳化MPEG-4和H.264的視訊編碼

Abstract

We propose four topics in terms of the spatial error concealment, temporal error concealment, hybrid error concealment approaches at the video decoder and memory management (MM) schemes at the video encoder. Highly compressed video bitstreams transmitted over error-prone communications networks can suffer from packet erasures. In order to avoid error-catalyzed artifacts from producing visible corruption of affected video frames, the use of error concealment (EC) at the video decoder becomes essential, especially in regard to wireless video transmission which can suffer packet loss more easily due to fluctuating channel conditions. Spatial error concealment (SEC) techniques are very useful in the recovery of impaired video sequences, especially in the presence of scene changes, irregular motion, and appearance or disappearance of objects. As errors occur in the first frame, the corrupted MBs must be recovered by utilizing SEC schemes in order to prevent the propagation of errors to the succeeding inter-coded frames. We propose two SEC methods; one conceals the variances of the different kinds of damaged Macroblocks (MBs) targeted at any condition, and the other is speed-up which utilizes a H.264 coding tool, directional spatial intra prediction, in order to conceal the entire spectrum of damaged MBs targeted at intra-coded block(s). Temporal error concealment techniques (TEC) are usually successful when there is continuous high correlation between the frames of the coded sequence. The proposed TEC techniques consist of a novel and unique mathematical model, the optimum regression plane, developed for the repair of damaged motion vectors, and the creation of a framework to perform the variable block size motion compensation based on predictive motion vectors in Laplacian distribution model space for H.264 decoder. We also propose an integrated Hybrid Error Concealment method consisting of both SEC and TEC techniques. Experiments performed using the proposed hybridization method of combining the above spatial and temporal estimation elements fulfilled the expectations of control-whole-scheme. The experimental results show that the proposed method offers excellent gains of up to 10.62dB compared to that of the Joint Model (JM) decoder for a wide range of benchmark sequences without any considerable increase in time demand. The external memory bandwidth for motion estimation is the most critical issue for the limited memory bandwidth and power consumption in the embedded video coding systems. The purpose of this paper is to propose an efficient and innovative memory bandwidth reduction scheme for the video encoder, using the data prediction and data reuse technique. Compared to those of traditional data reuse schemes for fast motion estimation, there is always a tradeoff between the reduction of memory bandwidth and the required internal memory size. Taking advantage of the function of the proposed data prediction and data reuse techniques for fast motion estimation, we significantly reduced the required memory bandwidth and internal memory size. Experiments performed using the proposed enhanced data prediction and data reuse scheme resulted in excellent gains, in some instances only using 37% of external memory bandwidth and 7% of internal memory size compared to the traditional data reuse scheme.