Block matching has been used for motion estimation and motion compensation in MPEG standards for years. While it has an acceptable performance in describing motion between frames, it requires quite a few bits to represent the motion vectors. In certain circumstances, the use of whole frame affine motion models would perform equally well or even better than block matching in terms of motion accuracy, while it results in the coding of only 6 parameters. In this paper, we modify an MPEG-4 codec by adding: (1) 6 affine model parameters to the frame header; and (2) mode selection among INTRA, SKIP, INTER-16/spl times/16, INTER-8/spl times/8, and GLOBAL-AFFINE modes by Lagrange optimal rate-distortion criteria. Simulation results demonstrate 10-20% decrease in bit-rate, compared to the MMS codec for an average coded P-frame with the same reconstruction PSNR.

In wireless video transmission, burst packet errors generally produce more catastrophic results than equal number of isolated errors. To miniimize the playback distortion it is crucial for the sender to know the packet errors at the receiver and then optimally schedule next transmissions. Unfortunately, in practice, feedback errors result in inaccurate observations of the receiving status. In this paper, we develop an optimal scheduling framework to minimize the expected distortion by first estimating the receiving status. Then, we jointly consider the source and channel characteristics and optimally choose the packets to transmit. The optimal transmission strategy is computed through a partially observable Markov decision process. The experimental results show that the proposed framework improves the average peak signal-to-noise ratio (PSNR) by 0.6-1.3 dB upon using a traditional system without packet scheduling. Moreover, we show that the proposed method smoothes out the bursty distortion periods and results in less fluctuating PSNR values.

The introduction of video objects (VOs) is one of the innovations of MPEG-4. The alpha-plane of a VO defines its shape at a given instance in time and hence determines the boundary of its texture. In packet-based networks, shape, motion, and texture are subject to loss. While there has been considerable attention paid to the concealment of texture and motion errors, little has been done in the field of shape error concealment. In this paper, we propose a post-processing shape error-concealment technique that uses geometric boundary information of the received alpha-plane. Second-order Hermite splines are used to model the received boundary in the neighboring blocks, while third order Hermite splines are used to model the missing boundary. The velocities of these splines are matched at the boundary point closest to the missing block. There exists the possibility of multiple concealing splines per group of lost boundary parts. Therefore, we draw every concealment spline combination that does not self-intersect and keep all possible results until the end. At the end, we select the concealment solution that results in one closed boundary. Experimental results demonstrating the performance of the proposed method and comparisons with prior proposed methods are presented.

Object-based video coding requires the transmission of the object shape. This shape is sent as a binary /spl alpha/-plane. In lossy packet-based networks, such as the Internet, this information has a nonnegligible probability of not arriving at the receiver, and hence its loss needs to be concealed. In this paper we propose a shape concealment technique utilizing Hermite splines. The algorithm has the following steps: (I) the received boundary is detected and the lost boundary parts are grouped using the packet loss pattern. (II) for each of these lost boundary parts, the received boundary points that border the area of the lost boundary parts are collected. These boundary points are then modelled by a second order Hermite spline. This model is subsequently used to match the velocity along the received boundary with the velocity of the concealing cubic Hermite spline. (Ill) since in most cases there are more than one concealing splines we draw every spline combination that does not result in an intersection and keep all possible results until the end. (IV) if there are more than one possible solutions we select the one that results in one overall closed nonintersecting boundary and fill the interior of the boundary to get the concealed /spl alpha/-plane. Experimental results which demonstrate and compare the performance of the proposed concealment method are given at the end of the paper.

The encoding of shape information is a distinguishing feature of MPEG-4. In error prone communication networks, it is important and efficient to conceal shape errors spatially, so as to avoid propagation of errors in the video frames. The proposed system first defines the missing area's four rectangular neighbors. It then detects in the neighbors the lines that intersect the borders and redefines them in a geometric coordinate system. These lines are paired under some optimization objective so that they connect smoothly in the missing area. Each pair is extrapolated and corrected recursively until a close curve is formed. Test results on various sequences under various error rates are presented and compared with other shape concealment methods.