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This paper presents a 3-D shape-adaptive directional wavelet coding technique for object-based scalable video coding. This technique includes 3-D object-based directional threading and extensions of weighted adaptive lifting (WAL) scheme. The 3-D object-based directional threading, which unifies the concept of temporal motion threading and 2-D spatial directional threading, provides the opportunities to align a series of video object planes to form a 3-D video object and exploit the spatio-temporal correlation inside the 3-D video object. The WAL scheme, which is extended from 2-D frame-based image coding to 3-D object-based video coding, is employed to decompose the 3-D video object into a 3-D multispatio-temporal resolution video object pyramid for object-based scalable video coding. Experimental results show that the proposed 3-D shape-adaptive directional wavelet coding technique consistently outperforms MPEG-4 and other wavelet-based schemes for coding arbitrarily shaped video objects. Index Terms--Arbitrarily shaped video object, directional wavelet transform, object-based coding, scalable video coding, weighted adaptive lifting (WAL), 3-D directional threading.

Voice over Internet protocol (VoIP) is one of the most important applications for IEEE 802.11 wireless local area networks (WLANs). For network planners who deploy VoIP over WLANs, one of the important issues is the VoIP capacity. Directly implementing VoIP over infrastructure WLANs will create the bottleneck problem at the access point (AP). In this paper, we propose the use of the service differentiation provided by the new IEEE 802.11e standard to solve the bottleneck problem and improve voice capacity. In particular, we propose the allocation of a higher priority access category (AC) to the AP while allocating lower priority AC to mobile stations. We develop a simple Markov chain model, which considers the important enhanced distributed channel access (EDCA) parameters and the channel errors under saturation and nonsaturation conditions. Based on the developed analytical model, we analyze the performance of VoIP over EDCA. By appropriately selecting the EDCA parameters, we are able to differentiate the services for the downlink and uplink. The experimental results are very promising. With the adjustment of only one EDCA parameter, we improve the VoIP capacity by 20%-30%. Index Terms--Enhanced distributed channel access (EDCA), IEEE 802.11e wireless local area networks (WLANs), medium access mechanisms, service differentiation, voice capacity, voice over Internet protocol (VoIP).

A cross-layer design for optimizing 3-D wavelet scalable video transmission over the IEEE 802.11e networks is proposed. A thorough study on the behavior of the IEEE 802.11e protocol is conducted. Based on our findings, all timescales rate control is developed featuring a unique property of soft capacity support for multimedia delivery. The design consists of a macro timescale and a micro timescale rate control schemes residing at the application layer and the network sublayer respectively. The macro rate control uses bandwidth estimation to achieve optimal bit allocation with minimum distortion. The micro rate control employs an adaptive mapping of packets from video classifications to appropriate network priorities which preemptively drops less important video packets to maximize the transmission protection to the important video packets. The performance is investigated by simulations highlighting advantages of our cross-layer design. Index Terms--Multimedia transmission, network performance analysis, scalable video, wireless LAN.

This paper describes a unified framework of bit-rate control for binary and gray-level shape coding. An exponential rate-distortion model is proposed for binary shape and used in the bit-rate control. An approximation method is applied for finer distortion scale adjustment by adjusting the conversion ratio at the binary alpha block level. Since the gray-level shape is encoded as its support information and the alpha plane information, the rate-quantizer relationship of the alpha plane is modeled. The bit-rate control is then able to adjust the quantizer of the alpha plane for the bit-rate control purpose. The extension for video object (VO) coding is also studied. In this bit-rate control approach, a buffer feedback controller is employed to determine the target bit rates for different sources, i.e., binary shape, gray-level shape, and texture. Accordingly, the distortion scales of different sources are adjusted based on their rate-distortion relationships to maintain a stable encoder buffer. The advantages of the proposed method are demonstrated through various tests for different scenarios. Overall, the algorithm can efficiently encode the shape information and shows a good performance for VO coding. Index Terms--Binary shape, gray-level shape, MPEG-4, rate control, rate-distortion, shape coding.

This paper extends the lifting-based motion threading (MTh) technique from the frame-based coding to the object-based coding, attracted by the unique advantages of the object-based coding that do not exist in other coding schemes. The boundary effects, which exist in spatial and temporal wavelet transforms due to the manner of object-based coding, are well suppressed by 3-D shape-adaptive discrete wavelet transform (3D SA-DWT) via the lifting implementation in a unified framework. Based on the proposed object-based MTh technique, a 3-D object-based scalable wavelet video coder is developed. Experimental results show that the proposed coder achieves good performance compared with the existing object-based coders and provides the scalability functionality at the same time. Index Terms--Boundary effects, object-based motion threading, wavelet video object coding, 3-D shape-adaptive discrete wavelet transform (3D SA-DWT).

In this paper, we address the key problem in real-time video coding, the rate-distortion (R-D) tradeoff. As most video coding applications employ color images, we analyze the R-D modeling problem of the color image sequence. We investigate that the R-D characteristics of color video signal in traditional transform-based video coding systems should be modeled for the luminance and chrominance components separately. So we propose separable R-D models for color video coding. The feedback from the encoder buffer is analyzed by a control-theoretic adaptation approach to avoid buffer overflow and underflow. To achieve smooth video quality and satisfy the delay constraints in real-time applications, a novel R-D tradeoff controller is designed. In the proposed R-D tradeoff framework, both the quality variation and buffer safety are considered. Extensive simulation results demonstrate that the proposed approach can achieve smooth video quality without sacrificing overall quality while efficiently utilize the bandwidth without buffer overflow or underflow. Index Terms--Buffer control, H.264, rate control, rate-distortion (R-D) model, R-D tradeoff, video coding.

The conventional multiview video coding (MVC) schemes, utilizing both neighboring temporal frames and view frames as possible references, have only shown a slight gain over those using temporal frames alone in terms of coding efficiency. The reason for this is that the neighboring temporal frames exhibit stronger correlation with the current frame and the view frames often fail to be selected as references. This paper proposes an elegant MVC framework using high dimensional wavelet, which rightly matches the inherent high dimension property of multiview video. It also makes a better usage of both temporal and view correlations thanks to the hierarchical decomposition. Besides the proposed framework, this paper also investigates MVC coding from the following aspects. First, a disparity-compensated view filter (DCVF) with pixel alignment is proposed, which can accommodate both global and local view disparities among view frames. The proposed DCVF and the existing motion-compensated temporal filter (MCTF) unify the view and temporal decompositions as a generic lifting transform. Second, an adaptive decomposition structure based on the analysis of the temporal and view correlations is proposed. A Lagrangian cost function is derived to determine the optimum decomposition structure. Third, the major components of the proposed MVC coding are figured out, including macroblock type design, subband coefficient coding, and rate allocation. Extensive experiments are carried out on the MPEG 3DAV test sequences and the superior performance of the proposed MVC coding is demonstrated. In addition, the proposed MVC framework can easily support temporal, spatial, SNR, as well as view scalabilities. Index Terms--Global and local motion alignment, high dimensional wavelet, lifting, multiview video coding (MVC).

In this paper, we investigate optimal frame-selection algorithms based on dynamic programming for delivering stored variable bit rate (VBR) video under both bandwidth and buffer size constraints. Our objective is to find a feasible set of frames that can maximize the video's accumulated motion values without violating any constraint. It is well known that dynamic programming has high complexity. In this research, we propose to eliminate nonoptimal intermediate frame states, which can effectively reduce the complexity of dynamic programming. Moreover, we propose a reverse frame selection (RFS) algorithm, where the selection starts from the last frame and ends at the first frame. Compared with the conventional dynamic programming-based forward frame selection, the RFS is able to find all of the optimal results for different preloads in one round. We further extend the RFS scheme to solve the problem of frame selection for VBR channels. In particular, we first perform the RFS algorithm offline, and the complexity is modest and scalable with the aids of frame stuffing and nonoptimal state elimination. During online streaming, we only need to retrieve the optimal frame-selection path from the pregenerated offline results, and it can be applied to any VBR channels as long as the VBR channels can be modeled as piecewise CBR channels. Experimental results show good performance of our proposed algorithms. Index Terms--Bandwidth smoothing, dynamic programming, motion awareness, optimal frame selection, variable bit rate (VBR) channels, VBR video delivery.

In this paper, we present a uniform framework for optimal multiple video object bit allocation in MPEG-4. We combine the rate-distortion (R-D) models for the texture and shape information of arbitrarily shaped video objects to develop the joint texture-shape R-D models. The dynamic programming technique is applied to optimize the bit allocation for the multiple video objects. The simulation results demonstrate that the proposed joint texture-shape optimization algorithm outperforms the MPEG-4 verification model on the decoded picture quality. Index Terms--Bit ailocation, joint texture-shape optimization, MPEG-4, multiple video object, rate control, rate-distortion (R-D).

In this letter, we explore the rate-distortion (R-D) characteristics of binary shape information in the MPEG-4 standard. The shape coding scheme is a block-based context-based arithmetic encoding approach and distortion is introduced by down and up sampling. Generally, the shape bit rate and nonnormalized distortion increase in proportion with the number of border blocks. At any given resolution scale, the more complex an object, the more distortion that is introduced. Consequently, we propose an R-D model based on the parameters derived from the border blocks and a block-based shape complexity for the video object. The computational complexity is much lower than other existing methods. Experimental results show that it can accurately predict the bit rate and distortion of the binary shape for rate control purposes. Index Terms--MPEG-4, rate distortion (R-D), shape coding.