Ñæàòèå âèäåî - Streaming
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Àíãëèéñêèå ìàòåðèàëû |
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| William Butera and V. Michael Bove, Jr. | The Coding Ecology: Image Coding via Competition Among Experts |
Abstract—We consider the image-coding problem as a competitive ecology of specialists, each vying for the task of coding a portion of an image. Each specialist, or expert, derives its competitive advantage from its ability to concisely describe an underlying visual event (e.g., shadows, motion, occluding objects). In this paper, the metaphor of an auction informs the design of a predictive coder. Experts locate candidate regions of support, characterize the activity within, and submit their proposals in the form of bids passed along to an auctioneer. We describe the designs for six such experts, and examine candidate strategies for the decision unit (the auctioneer).We define protocols for comparing the bids, and compare overall coding performance using several examples. RAR 1000 êáàéò |
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| JongWon Kim, Young-Gook Kim, HwangJun Song, Tien-Ying Kuo, Yon Jun Chung, and C.-C. Jay Kuo, Fellow | TCP-Friendly Internet Video Streaming Employing Variable Frame-Rate Encoding and Interpolation |
Abstract—It has been previously reported that variable bit rate video traffic displays signs of long-range dependence [4], [13], which is defined within the framework of weak stationarity. The concept of weak stationarity is of fundamental practical interest, because it implies the existence and independence with time of mean and autocovariance. Since mean and variance might be used as parameters for policing the traffic stream on a broadband communication network, it is important to verify the underlying assumption of weak stationarity. The results presented in this paper strongly call into question this assumption. As a possible explanation, we offer shifting level processes which are asymptotically weakly stationary for infinite sample sizes. RAR 771 êáàéò |
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| Tolga K. Capin, Joaquim Esmerado, and Daniel Thalmann | A Dead-Reckoning Technique for Streaming Virtual Human Animation |
Abstract—In networked virtual environments (NVE’s), users are represented by their virtual embodiments. The articulated structure of these embodiments introduces a new complexity in the representation and streaming of animations, especially when the number of participants in the simulation increases. This requires real-time algorithms to decrease networking overhead. The dead-reckoning technique is a way to reduce the required bit rate, and has been used for simple nonarticulated objects in popular NVE systems. In this paper, we introduce a deadreckoning technique for articulated virtual human figures, based on the MPEG-4 body animation specification, using Kalman filtering. RAR 122 êáàéò |
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| Jianfei Cai and Chang Wen Chen | Robust Joint Source-Channel Coding for Image Transmission Over Wireless Channels |
Abstract—In this letter, we present a fixed-length robust joint source-channel coding (RJSCC) scheme for transmitting images over wireless channels. The system integrates a joint source-channel coding (JSCC) scheme with all-pass filtering source shaping to enable robust image transmission. In particular, we are able to incorporate both transition probability and bit error rate of a bursty channel model into an end-to-end rate-distortion (R-D) function to achieve an optimum tradeoff between source coding accuracy and channel error protection under a fixed transmission rate. Experimental results show that the proposed scheme can achieve not only high peak signal-to-noise ratio performance, but also excellent perceptual quality, especially when the channel mismatch occurs. RAR 211 êáàéò |
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| Maja Bystrom, Vasu Parthasarathy, and James W. Modestino | Corrections to “Hybrid Error Concealment Schemes for Broadcast Video Transmission over ATM Networks” |
RAR 52 êáàéò |
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| Pedro A. A. Assunção and Mohammed Ghanbari, | Buffer Analysis and Control in CBR Video Transcoding |
Abstract—In video distribution services, various networks of different capacity may be linked together to form the branches of a multicasting tree. In order to efficiently use the available bandwidth of each subnetwork, a video transcoder capable of reducing the bit rate of the incoming bit stream must be used at those nodes whose output links have less bandwidth than the input one. In this paper, we analyze the buffering implications of inserting a video transcoder within the transmission path. For transcoders with either fixed or variable compression ratio, we show that the encoder buffer size can be maintained as if no transcoder existed while the decoder has to modify its own buffer size according to both the bit rate conversion ratio and transcoder buffer size.We derive the conditions that have to be met by both the encoder and transcoder buffers for preventing the decoder buffer from underflowing or overflowing. Furthermore, based on the characteristics of constant bit rate (CBR) MPEG coded video, we show that efficient bit rate control can be implemented in CBR video transcoders such that the picture quality of transcoded sequences is practically the same as those directly encoded from the original sequence at the same reduced bit rates. RAR 198 êáàéò |
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| Tae-yong Kim, Byeong-hee Roh, and Jae-kyoon Kim, | Bandwidth Renegotiation with Traffic Smoothing and Joint Rate Control for VBR MPEG Video Over ATM |
Abstract—Variable bit-rate (VBR) MPEG video traffic is highly bursty due to group of pictures structure, and shows time-variant statistical characteristics due to scene changes. These characteristics make it more difficult to manage network resources, and leads to the significant reduction in network utilization. In this paper, we deal with the issues related to efficiently transmitting VBR MPEG video traffic over asynchronous transfer mode networks, while maintaining consistent visual quality and improving network utilization on the basis of real-time applications. First, we propose a joint encoder and channel-rate control scheme that comply with not only negotiated traffic parameters, but also constraints imposed by encoder and decoder buffers. Second, we propose a dynamic bandwidth renegotiation method by combining the above scheme with a traffic smoothing method that can make the peak rate close to the sustainable rate. The efficiencies of the proposed methods are compared with a few other competitive schemes such as transmission methods for unconstrained VBR and the constant bit-rate scheme with average bandwidth equal to that of the proposed methods. RAR 336 êáàéò |
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| Haitao Zheng and K. J. Ray Liu, | The Subband Modulation: A Joint Power and Rate Allocation Framework for Subband Image and Video Transmission |
Abstract—A new approach of reliable image and video transmission over noisy channels is proposed. For subband decomposed image and video, combined source coding and channel modulation design can achieve high compression efficiency and preferable quality. Further performance gain is obtained by multiresolution modulation as well as a bit-remapping scheme that assigns efficient mapping from each source codeword to channel modulation points. We show that the combined source coding and modulation design outperforms conventional approaches, which design source coding and modulation separately. A simple channel distortion approximation is derived by applying a bitremapping scheme, which allows the power allocation to be employed to further enhance the performance. Compared to the joint source and channel coding with a binary phase shift keying modulation system and fixed modulation with the one-to-one intelligent mapping system, the proposed system performs better in a middle-range signal-to-noise ratio and low channel bandwidth. The simulation is carried out on additive white Gaussian noise channels. RAR 493 êáàéò |
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| Jiro Katto, and Mutsumi Ohta | System Architecture for Synthetic/Natural Hybrid Coding and Some Experiments |
Abstract—This paper presents a system architecture for synthetic/ natural hybrid coding toward future visual services. Scenedescription capability, terminal architecture, and network architecture are discussed by taking account of recent standardization activities: MPEG, VRML, ITU-T, and IETF. A consistent strategy to integrate scene-description capability and streaming technologies is demonstrated. Experimental results are also shown, in which synthetic/natural integration is successfully carried out. RAR 325 êáàéò |
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| Jianhua Lu, Khaled Ben Letaief, and Ming L. Liou, Fellow | Robust Video Transmission over Correlated Mobile Fading Channels |
Abstract— In this paper, we develop a unique set of techniques to support reliable and efficient video transmission over bandwidth-limited mobile networks. The video coder is based on the H.263 coding standard, while its transmission system design is based on a joint study of combined source and channel coding, diversity reception, and pre/postprocessing techniques. In particular, a finite-state Markov model for representing a correlated fading channel with diversity is developed. Based on this model, a recursive algorithm is further devised for an efficient estimation of block-code performance. By doing so, an important means for finding proper diversity and channel coding schemes for correlated video data in correlated fading channels is obtained. In addition, robust decoding together with a combined spatial-temporal concealment is employed to mitigate the effects of decoding mismatch caused by residual errors. Simulation results confirm that the proposed system can significantly reduce the bursty error effects on the H.263 coded video data while maintaining high transmission efficiency. RAR 562 êáàéò |
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| Jong Wook Park and Sang Uk Lee | Recovery of Corrupted Image Data Based on the NURBS Interpolation |
Abstract—This paper presents a recovery technique for the image block data corrupted by transmission losses, employing the two-dimensional non-uniform rational B-spline (NURBS) function. In our approach, the control grid points which generate the best approximated surface of the neighboring image data are obtained by an optimization technique. To recover the edge components in the corrupted block more faithfully, the edge linking algorithm is utilized for the estimation of the edge components, and the interpolation algorithms are modified to enhance the edge components. Computer simulation results show that the contents of the corrupted image block data, including the edge components, can be recovered more faithfully than the conventional algorithms. RAR 399 êáàéò |
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| Doo-Man Chung and Yao Wang, | Multiple Description Image Coding Using Signal Decomposition and Reconstruction Based on Lapped Orthogonal Transforms |
Abstract—This paper considers the use of multiple description coding (MDC) for image transmission in communication systems where long burst errors and sometimes complete channel failures are inevitable. A general framework for MDC is proposed, which uses nonhierarchical signal decomposition at the encoder and image reconstruction at the decoder. A realization of this framework using lapped orthogonal transforms (LOT’s) is developed. In the encoder, the bitstream generated by a conventional LOTbased image coder is decomposed so that each description consists of a subsampled set of the coded LOT coefficient blocks. In the decoder, instead of using the inverse LOT directly, a novel image reconstruction technique is employed, which makes use of the constraints between adjacent LOT coefficient blocks and the smoothness property of common image signals. To guarantee a satisfactory reconstruction quality, the transform should introduce a desired amount of correlation among adjacent LOT coefficient blocks. The tradeoff between coding efficiency and reconstruction quality obtainable by using different LOT bases is investigated. RAR 2056 êáàéò |
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| Bo Shen, Ishwar K. Sethi, and Bhaskaran Vasudev | Adaptive Motion-Vector Resampling for Compressed Video Downscaling |
Abstract—Digital video is becoming widely available in compressed form, such as a motion JPEG or MPEG coded bitstream. In applications such as video browsing or picture-in-picture, or in transcoding for a lower bit rate, there is a need to downscale the video prior to its transmission. In such instances, the conventional approach to generating a downscaled video bitstream at the video server would be to first decompress the video, perform the downscaling operation in the pixel domain, and then recompress it as, say, an MPEG bitstream for efficient delivery. This process is computationally expensive due to the motion-estimation process needed during the recompression phase. We propose an alternative compressed domain-based approach that computes motion vectors for the downscaled (N= 2.N= 2) video sequence directly from the original motion vectors for the N . N video sequence. We further discover that the scheme produces better results by weighting the original motion vectors adaptively. The proposed approach can lead to significant computational savings compared to the conventional spatial (pixel) domain approach. The proposed approach is useful for video severs that provide quality of service in real time for heterogeneous clients. and it is in this scenario that the video server has to perform downscaling of the compressed video in real time. RAR 318 êáàéò |
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| Yi-Huang Han and Jin-Jang Leou | Detection and Correction of Transmission Errors in JPEG Images |
Abstract—In this study, the detection and correction approach to transmission errors in Joint Photographic Experts Group (JPEG) images using the sequential discrete cosine transform (DCT)-based mode of operation is proposed. The objective of the proposed approach is to eliminate transmission errors in JPEG images. Here a transmission error may be either a single-bit error or a burst error containing N successive error bits. For an entropy-coded JPEG image, a single transmission error in a codeword will not only affect the underlying codeword, but may also affect subsequent codewords. Consequently, a single error in an entropy-coded system may result in a significant degradation. To cope with the synchronization problem, in the proposed approach the restart capability of JPEG images is enabled, i.e., the eight unique restart markers (synchronization codewords) are periodically inserted into the JPEG compressed image bitstream. Transmission errors in a JPEG image are sequentially detected both when the JPEG image is under decoding and after the JPEG image has been decoded. When a transmission error or equivalently a corrupted restart interval is detected, the proposed error correction approach simply performs a sequence of bit inversions and redecoding operations on the corrupted restart interval and selects the “best” feasible redecoding solution by using a proposed cost function for error correction. Based on the simulation results obtained in this study, the proposed approach can recover highquality JPEG images from the corresponding corrupted JPEG images at bit error rates (BER’s) up to approximately 0.4%. This shows the feasibility of the proposed approach. RAR 303 êáàéò |
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| Li-Jae Wang and Jin-Jang Leou | Detection and Correction of Transmission Errors in Pyramid Images |
Abstract—In this study, two detection and correction approaches to protection from transmission errors in pyramid images are proposed. For entropy-coded pyramid images, a single transmission error in a codeword will not only affect the underlying codeword, but also may affect subsequent codewords. Consequently, a single error in an entropy-coded system may result in significant degradation. In this paper, two types of variable-length codes with the synchronization capability are proposed to encode two types of pyramid images, namely, the difference pyramid and the reduced-difference pyramid, to overcome the synchronization problem. The proposed approaches detect transmission errors by examining error checking conditions. When a transmission error is detected, a sequence of bit inversions and redecoding processes is performed on the corrupted part of the compressed image bitstream until a feasible redecoding solution is found. The simulation results show significant quality improvement. RAR 167 êáàéò |
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| Vasudevan Parthasarathy, James W. Modestino, Fellow, and Kenneth S. Vastola, | Design of a Transport Coding Scheme for High-Quality Video over ATM Networks |
Abstract— In this paper, we explore the design of forward error control (FEC)-based error concealment schemes for digital video transmission on ATM networks. In particular, we study the impact of code selection on the overall performance and provide a judicious code selection strategy. The use of FEC provides an active and powerful means of recovery from packet loss which is particularly useful when the encoded video material has high motion and scene changes. The best technique for applying FEC is to throttle the source coding rate so that the overall transmission rate after FEC application equals the original unprotected rate. However, the resulting performance then depends on the particular code selected. A well-chosen code provides good protection while allowing little sacrifice in quality and at the same time satisfies specified delay constraints. Our results show that a single code is generally insufficient to provide good performance under all operating conditions. However, a small group of codes can be preselected, using the efficient code-selection strategy described here, which will provide efficient and robust performance over a wide range of channel conditions. We show that this simple code selection strategy is sufficient to select codes judiciously for a wide range of operating conditions and constraints. Employing this selection strategy, we demonstrate that moderate length codes are sufficient to provide good performance while meeting the imposed delay constraint. RAR 678 êáàéò |
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| Dapeng Wu, Yiwei Thomas Hou, Wenwu Zhu, Hung-Ju Lee, Tihao Chiang, Ya-Qin Zhang, Fellow, and H. Jonathan Chao, | On End-to-End Architecture for Transporting MPEG-4 Video Over the Internet |
Abstract—With the success of the Internet and flexibility of MPEG-4, transporting MPEG-4 video over the Internet is expected to be an important component of many multimedia applications in the near future. Video applications typically have delay and loss requirements, which cannot be adequately supported by the current Internet. Thus, it is a challenging problem to design an efficient MPEG-4 video delivery system that can maximize the perceptual quality while achieving high resource utilization. This paper addresses this problem by presenting an end-to-end architecture for transporting MPEG-4 video over the Internet. We present a framework for transporting MPEG-4 video, which includes source rate adaptation, packetization, feedback control, and error control. The main contributions of this paper are: 1) a feedback control algorithm based on Real Time Protocol (RTP) and Real Time Control Protocol (RTCP); 2) an adaptive source-encoding algorithm for MPEG-4 video which is able to adjust the output rate of MPEG-4 video to the desired rate; and 3) an efficient and robust packetization algorithm for MPEG video bit-streams at the sync layer for Internet transport. Simulation results show that our end-to-end transport architecture achieves good perceptual picture quality for MPEG-4 video under low bit-rate and varying network conditions and efficiently utilizes network resources. RAR 489 êáàéò |
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| Omid Fatemi and Sethuraman (Panch) Panchanathan, | Fractal Engine: An Affine Video Processor Core for Multimedia Applications |
Abstract—The recent advances in VLSI technology, high-speed processor designs, Internet/Intranet implementations, broadband networks (ATM and ISDN), and compression standards (JPEG, MPEG, H.261, H.263, and G.273) are leading to the popularity of multimedia applications. Examples include video over the Internet, interactive TV, distance learning, telemedicine, and digital libraries. Multimedia refers to a combination of various media types including text, audio, two-dimensional (2-D) and three-dimensional (3-D) graphics, animation, images, and video. Visual media (image, video, and graphics) proliferation in multimedia applications demands high-powered compute engines, large storage devices, and high-bandwidth networks for the processing, storage, and transport of image/video data. Visual media processing poses challenges from several perspectives, specifically from the points of view of real-time implementation and scalability. In this paper, we first present an overview and categorization of the various architectural approaches for multimedia processing. The fundamental operations involved in a majority of visual processing tasks are then derived. We propose an affine transform-processor-core-based video processor architecture called fractal engine that is capable of implementing the basic visual processing operations. Fractal engine is an open architecture, and is designed to be modular and scalable, and therefore has the potential to satisfy the heterogeneous computing requirements of the different media types in multimedia processing. Details of the individual modules of the fractal engine as well the implementation of the architecture in VHDL are also presented in this paper. RAR 411 êáàéò |
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| M. Grasse, M. R. Frater, and J. F. Arnold | Testing VBR Video Traffic for Stationarity |
Abstract—It has been previously reported that variable bit rate video traffic displays signs of long-range dependence [4], [13], which is defined within the framework of weak stationarity. The concept of weak stationarity is of fundamental practical interest, because it implies the existence and independence with time of mean and autocovariance. Since mean and variance might be used as parameters for policing the traffic stream on a broadband communication network, it is important to verify the underlying assumption of weak stationarity. The results presented in this paper strongly call into question this assumption. As a possible explanation, we offer shifting level processes which are asymptotically weakly stationary for infinite sample sizes. RAR 392 êáàéò |
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| Yiu-Wing Leung, | Congestion Control for Multipoint Videoconferencing |
Abstract—Multipoint videoconference service allows multiple and far-away conferees to conduct a meeting without leaving their offices. Variable-bit-rate video compression is attractive for videoconferencing, because it can provide a constant image quality and it can effectively utilize the communication bandwidth via statistical multiplexing. When some conferences temporarily generate heavy traffic to a link, congestion occurs and some video packets have to be discarded. Since the packets of different conferences are multicast to different number of conferees, the loss of different packet will affect different number of people. If we discard the packets sent to the smallest number of conferees, we can minimize the number of affected conferees to give the best mean quality of service, but the conference having a smaller number of conferees will suffer from a poorer quality of service. Therefore, we must consider both the mean quality of service and fairness in congestion control. In this paper,we propose a congestion-control strategy for multipoint videoconferencing. This strategy has a control parameter which we can tune to make a tradeoff between the mean quality of service and fairness. In addition, the strategy only involves some simple arithmetic and logic operations, and hence, it can be executed quickly for real-time congestion control. RAR 249 êáàéò |
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| Shugong Xu, Zailu Huang, and Yan Yao | An Analytically Tractable Model for Video Conference Traffic |
Abstract—In this letter, we propose an analytically tractable approach to model-compressed video traffic called C-DAR(1). The C-DAR(1) model combines an approach utilizing a discrete-time Markov chain with a continuous-time Markov chain.We show that this approach accurately models the distribution and exponential autocorrelation characteristics of video conferencing traffic. Also, we show that by comparing our analytical results against a simulation using actual video-conferencing data, our model provides realistic results. In addition to presenting this new approach, we address the effects of long-range dependencies (LRD) in the video traffic. Based on our analytical and simulation results, we are able to conclude that the LRD have minimal impact on videoconference traffic modeling. RAR 94 êáàéò |
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| Byeong-hee Roh, and Jae-kyoon Kim, | Starting Time Selection and Scheduling Methods for Minimum Cell Loss Ratio of Superposed VBR MPEG Video Traffic |
Abstract—The arrangement of I-picture starting times of multiplexed variable bit rate (VBR) MPEG videos may significantly affect the cell loss ratio (CLR) characteristics of superposed traffic. In this paper, we deal with the problems due to the starting time arrangement of VBR MPEG videos. VBR MPEG video traffic is modeled by a sequence with time-varying and periodic picture-type dependent rate envelopes. From extensive investigations into the relationships between the starting time arrangement and the queueing performance, it is shown that the average power of superposed VBR MPEG video traffic can be a good measure for the burstiness of the traffic. Then, we can derive a starting time selection method for a newly requested VBR MPEG video that can minimize the CLR as well as the peak cell rate of the superposed traffic including the new request itself, and an efficient scheduling method called MC-scheduling is also proposed as an application of the starting time selection method. The exactness and efficiencies of the proposed methods are shown by comparing them with other scheduling methods in terms of the smoothness and the CLR performances. RAR 321 êáàéò |
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| Q. T. Zhang, | A General AR-Based Technique for the Generation of Arbitrary Gamma VBR Video Traffic in ATM Networks |
Abstract—Modeling variable-bit-rate (VBR) video source traf- fic is a crucial issue to evaluate the end-to-end performance of transmitting video signals over asynchronous transfer mode (ATM) networks. Difficulties in source modeling arise from the fact that VBR video source traffic usually follows a gamma distribution with high correlation among adjacent data. Many researchers adopt autoregressive (AR) models driven by a Gaussian error process to account for such correlation. The problem is: due to the closure property of the Gaussian distribution, the traffic so generated is Gaussian rather than gamma. As a remedy, some researchers directly consider gamma AR models instead. RAR 288 êáàéò |
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| D. N. Serpanos, L. Georgiadis, and T. Bouloutas | MMPacking: A Load and Storage Balancing Algorithm for Distributed Multimedia Servers |
Abstract—In distributed multimedia servers where client requests for different video streams may have different probabilities, placement of video streams is an important parameter because it may result in unbalanced requests to the system’s stations, and thus to high blocking probabilities of requests. We present a method, MMPacking, to balance traffic load and storage use in a distributed server environment. Since different video streams are requested by clients with different rates, video stream replication is used to balance the traffic patterns of the stations; thus, the requests and I/O usage of the stations are balanced, since replication allows requests for the same video stream to be routed to different stations. RAR 213 êáàéò |
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| Wei Ding | Joint Encoder and Channel Rate Control of VBR Video over ATM Networks |
Abstract—Rate control is considered an important issue in video coding, since it significantly affects video quality. In this paper, we will discuss joint encoder and channel rate control for variable bit-rate (VBR) video over packet-switched ATM networks. Since variable bit-rate traffic is allowed in such networks, an open-loop encoder without rate control can generate consistent quality video. However, in order to improve statistical multiplexing gain (SMG), an encoder buffer is essential to meet traffic constraints imposed by networks and to smooth the highly variable video bitstream. Due to the finite buffer size, some forms of encoder rate control have to be enforced, and consequently, video quality varies. We argue that a rate control scheme has to balance both issues of consistent video quality on the encoder side and bitstream smoothness for SMG on the network side. RAR 491 êáàéò |
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| Jack Y. B. Lee | Concurrent Push—A Scheduling Algorithm for Push-Based Parallel Video Servers |
Abstract—Most existing commercial video servers are designed for a single server. Consequently, the capacity of the system in terms of maximum sustainable concurrent sessions is limited by the performance of the video server hardware. This paper proposes and analyzes the performance of a novel parallel video server architecture where video data are striped across an array of autonomous servers. The architecture allows one to build incrementally scalable video servers without video data replication. The proposed concurrent-push scheduling algorithm allows the system to integrate with quality of service guarantees provided by today’s switching networks. In this paper, the striping policy, the service model, and the concurrent-push scheduling algorithm are presented. A system model is constructed to quantify three performance metrics, namely, server buffer requirement, client buffer requirement, and system response time. Results show that a simple extension of the server-push service model does not perform well under the parallel video server architecture. To improve system performance, a novel extension of the grouped sweeping scheme called the asynchronous grouped sweeping scheme (AGSS) is introduced. To further increase the scalability of the architecture, a new subschedule striping scheme (SSS) is introduced. With the proposed AGSS and SSS, our parallel video server architecture can be scaled up to more than 10 000 concurrent users. RAR 287 êáàéò |
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| Hsueh-Ming Hang, and Jiann-Jone Chen | Source Model for Transform Video Coder and Its Application—Part I: Fundamental Theory |
Abstract—A source model describing the relationship between bits, distortion, and quantization step sizes of a large class of block-transform video coders is proposed. This model is initially derived from the rate-distortion theory and then modified to match the practical coders and real image data. The realistic constraints such as quantizer dead-zone and threshold coefficient selection are included in our formulation. The most attractive feature of this model is its simplicity in its final form. It enables us to predict the bits needed to encode a picture at a given distortion or to predict the quantization step size at a given bit rate. There are two aspects of our contribution: one, we extend the existing results of rate-distortion theory to the practical video coders, and two, the nonideal factors in real signals and systems are identified, and their mathematical expressions are derived from empirical data. One application of this model, as shown in the second part of this paper, is the buffer/quantizer control on a CCITT P .64 k coder with the advantage that the picture quality is nearly constant over the entire picture sequence. RAR 435 êáàéò |
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| Jiann-Jone Chen and Hsueh-Ming Hang, | Source Model for Transform Video Coder and Its Application—Part II: Variable Frame Rate Coding |
Abstract—In the first part of this paper, we derive a source model describing the relationship between bits, distortion, and quantization step size for transform coders. Based on this source model, a variable frame rate coding algorithm is developed. The basic idea is to select a proper picture frame rate to ensure a minimum picture quality for every frame. Because our source model can predict approximately the number of coded bits when a certain quantization step size is used, we could predict the quality and bits of coded images without going through the entire realcoding process. Therefore, we could skip the right number of picture frames to accomplish the goal of constant image quality. Our proposed variable frame rate coding schemes are simple but quite effective as demonstrated by simulation results. The results of using another variable frame rate scheme, Test Model for H.263 (TMN-5), and the results of using a fixed frame rate coding scheme, Reference Model 8 for H.261 (RM8), are also provided for comparison. RAR 435 êáàéò |
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| Shugong Xu and Zailu Huang | A Gamma Autoregressive Video Model on ATM Networks |
Abstract—Several works have concluded that the number of cells per frame of variable bit-rate (VBR) video teleconference follows a gamma distribution. But few video models meet this characteristics. In this paper we propose a novel video model, called first-order autoregressive (AR) gamma sequence, in which random variables are marginally distributed as gamma variables. We give the definition of a GAR model and a simple realization method of GAR(1). Parameter estimation methods are studied, too. Simulation results show that our model can meet the characteristics dom variables are marginally distributed as gamma variables. RAR 152 êáàéò |
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| Qin-Fan Zhu, Louis Kerofsky, and Marshall B. Garrison | Low-Delay, Low-Complexity Rate Reduction and Continuous Presence for Multipoint Videoconferencing |
Abstract— In this paper, we propose new methods and architecture for low-delay, low-complexity video bit-rate reduction and continuous presence for multipoint videoconferencing. Rate reduction is performed in the discrete cosine transform (DCT) domain to achieve both low delay and low complexity. Requantization is applied to the originally quantized DCT coefficients, and the requantization errors are stored in a frame buffer in the DCT domain instead of the pixel domain. Skipped macroblocks in the original coded bitstream are processed to improve picture quality. The QCIF-to-CIF combiner is used to realize continuous presence. Asymmetric frame rates and pipelined combination on the group-of-blocks level lead to significantly reduced insertion delay compared to the published methods in the literature. Both simulation and real-time implementation results are reported to validate the proposed methods and architecture. RAR 266 êáàéò |
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| Dimitrios N. Serpanos, and A. Bouloutas | Centralized versus Distributed Multimedia Servers |
Abstract—The organization of multimedia servers is important in the design of low-cost high-performance multimedia application environments. Considering video services as highly demanding applications in a multimedia environment, we analyze and compare centralized and distributed architectures for multimedia video servers. Comparisons are made in terms of the blocking probability of a video client’s request, considering as important parameters the input/output capacity of the system and the amount of storage. Through a combination of analytical results and simulations, we conclude that in general a centralized architecture is preferable. The results indicate, however, that in a distributed architecture containing a large number of powerful servers, performance is similar to the centralized architecture under high load conditions, while the blocking probabilities are quite small under light load conditions. Furthermore, centralized and distributed server architectures become equivalent when large amounts of storage are added to the latter or when their input/output capacity is significantly increased. The results indicate that in many practical environments, factors other than performance, such as cost of management, security, and fault tolerance, will influence the choice for the appropriate server configuration. RAR 250 êáàéò |
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