Ñæàòèå âèäåî - Ñòàíäàðòû
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| Àâòîðû | Íàçâàíèå ñòàòüè | Îïèñàíèå | Ðåéòèíã |
| Ñåìåíþê Â. | Ñîâðåìåííûå ìåòîäû è ñòàíäàðòû ýêîíîìíîãî êîäèðîâàíèÿ âèäåîèíôîðìàöèè | Ââîäíûé îáçîð ñòàíäàðòîâ MPEG-4, H.264 è MVC
Ñàíêò-Ïåòåðáóðã, 2002. PDF 212 êáàéò |
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| Àâòîðû | Íàçâàíèå ñòàòüè | Îïèñàíèå | Ðåéòèíã |
| S. Olivieri, L. Albani ,G. de Haan | A LOW{COMPLEXITY RECURSIVE MOTION ESTIMATION ALGORITHM FOR H.263 VIDEO CODING1 |
Abstract - The key element in realizing low cost real{time software implementations of a H.263 videoconferencing system is a fast motion estimation algorithm, which only slightly decreases coding e.ciency. We propose a spatio{temporal recursive estimator that combines an excel- lent coding e.ciency with a high computational e.ciency. Experiment- ally, the new algorithm proves to be comparable to full{search block matching when encoding typical videoconferencing sequences in pres- ence of additive noise, even though the computational burden has been greatly reduced. RAR 484 êáàéò |
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| Stefano Olivieriy, Gerard de Haan z, and Luigi Albaniy | Noise{robust Recursive Motion Estimation for H.263{based videoconferencing systems |
The key element in realizing low cost real{time software implementations of a H.263 video- conferencing system is a fast motion estimation algorithm, which only slightly decreases coding e.ciency. We propose a spatio{temporal recursive estimator that combines an excellent coding e.ciency with a high computational e.ciency. Experimentally, the new algorithm proves to be comparable to full{search block matching when encoding typical videoconferencing sequences in presence of additive noise, even though the computational burden has been greatly reduced. RAR 138 êáàéò |
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| Xudong Song, Tihao Chiang, Xiaobing Lee, and Ya-Qin Zhang, Fellow | New Fast Binary Pyramid Motion Estimation for MPEG2 and HDTV Encoding |
Abstract—A novel Fast Binary Pyramid Motion Estimation (FBPME) algorithm is presented in this paper. The proposed FBPME scheme is based on binary multiresolution layers, exclusive- or (XOR) Boolean block matching, and a -scale tiling search scheme. Each video frame is converted into a pyramid structure of 1 binary layers with resolution decimation, plus one integer layer at the lowest resolution. At the lowest resolution layer, the -scale tiling search is performed to select initial motion vector candidates. Motion vector fields are gradually refined with the XOR Boolean block-matching criterion and the -scale tiling search schemes in higher binary layers. FBPME performs several thousands times faster than the conventional full-search block-matching scheme at the same PSNR performance and visual quality. It also dramatically reduces the bus bandwidth and on-chip memory requirement. Moreover, hardware complexity is low due to its binary nature. Fully functional software MPEG-2 MP@ML encoders and Advanced Television Standard Committee High Definition Television encoders based on the FBPME algorithm have been implemented. FBPME Hardware architecture has been developed and is being incorporated into single-chip MPEG encoders. A wide range of video sequences at various resolutions has been tested. The proposed algorithm is also applicable to other digital video compression standards such as H.261, H.263, and MPEG4. RAR 563 êáàéò |
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| Barry G. Haskell, Fellow, Paul G. Howard, Yann A. LeCun, Atul Puri, J?oern Ostermann, M. Reha Civanlar, Lawrence Rabiner, Fellow, Leon Bottou, and Patrick Haffner | Image and Video Coding—Emerging Standards and Beyond |
Abstract— In this paper, we make a short foray through coding standards for still images and motion video. We first briefly discuss standards already in use, including: Group 3 and Group 4 for bilevel fax images; JPEG for still color images; and H.261, H.263, MPEG-1, and MPEG-2 for motion video. We then cover newly emerging standards such as JBIG1 and JBIG2 for bilevel fax images, JPEG-2000 for still color images, and H.263+ and MPEG-4 for motion video. Finally, we describe some directions currently beyond the standards such as hybrid coding of graphics/photo images, MPEG-7 for multimedia metadata, and possible new technologies. RAR 921 êáàéò |
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| Peter Cherriman, Choong Hin Wong, and Lajos Hanzo | Turbo- and BCH-Coded Wide-Band Burst-by-Burst Adaptive H.263-Assisted Wireless Video Telephony |
Abstract—The video performance benefits of burst-by-burst adaptive modulation are studied, employing a higher-order modulation scheme when the channel is favorable, in order to increase the system’s bits per symbol capacity and conversely, invoking a more robust lower order modulation scheme when the channel exhibits inferior channel quality. It is shown that due to the proposed adaptive modem mode switching regime, a seamless video-quality versus channel quality relationship can be established, resulting in error-free video quality right across the operating channel signal-to-noise ratio (SNR) range. The main advantage of the proposed burst-by-burst adaptive transceiver technique is that irrespective of the prevailing channel conditions, the transceiver achieves always the best possible source-signal representation quality—such as video, speech, or audio quality—by automatically adjusting the achievable bitrate and the associated multimedia source-signal representation quality in order to match the channel quality experienced. This is achieved on a near-instantaneous basis under given propagation conditions in order to cater for the effects of path loss, fast-fading, slow-fading, dispersion, co-channel interference, etc. Furthermore, when the mobile is roaming in a hostile out-doors—or even hilly terrain—propagation environment, typically low-order low-rate modem modes are invoked, while in benign indoor environments, predominantly the high-rate high source-signal representation quality modes are employed. RAR 188 êáàéò |
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| Marek Doman´ski, Adam £uczak, and S³awomir Mac´kowiak | Spatio-Temporal Scalability for MPEG Video Coding |
Abstract—The existing and standardized solutions for spatial scalability are not satisfactory, therefore new approaches are very actively explored recently. The goal of this paper is to improve spatial scalability of MPEG-2 for progressive video. In order to avoid problems with too large bitstreams of the base layer produced by some of the hitherto proposed spatially scalable coders, spatio-temporal scalability is proposed for video compression systems. It is assumed that a coder produces two bitstreams, where the base-layer bitstream corresponds to pictures with reduced both spatial and temporal resolution while the enhancement layer bitstream is used to transmit the information needed to retrieve images with full spatial and temporal resolution. In the base layer, temporal resolution reduction is obtained by B-frame data partitioning, i.e., by placing each second frame (B-frame) in the enhancement layer. Subband (wavelet) analysis is used to provide spatial decomposition of the signal. Full compatibility with the MPEG-2 standard is ensured in the base layer. As compared to single-layer MPEG-2 encoding at bit rates below 6 Mbits/s, the bitrate overhead for scalability is less than 15% in most cases. RAR 131 êáàéò |
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| Hung-Ju Lee, Tihao Chiang, and Ya-Qin Zhang, Fellow | Scalable Rate Control for MPEG-4 Video |
Abstract—This paper presents a scalable rate control (SRC) scheme based on a more accurate second-order rate-distortion model. A sliding-window method for data selection is used to mitigate the impact of a scene change. The data points for updating a model are adaptively selected such that the statistical behavior is improved. For video object (VO) shape coding, we use an adaptive threshold method to remove shape-coding artifacts for MPEG-4 applications. A dynamic bit allocation among VOs is implemented according to the coding complexities for each VO. SRC achieves more accurate bit allocation with low latency and limited buffer size. In a single framework, SRC offers multiple layers of controls for objects, frames, and macroblocks (MBs). At MB level, SRC provides finer bit rate and buffer control. At multipleVOlevel, SRC offers superiorVOpresentation for multimedia applications. The proposed SRC scheme has been adopted as part of the International Standard of the emerging ISO MPEG-4 standard [1], [2]. RAR 568 êáàéò |
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| Pao-Chi Chang and Tien-Hsu Lee | Precise and Fast Error Tracking for Error-Resilient Transmission of H.263 Video |
Abstract—In this letter, a precise error-tracking scheme for robust transmission of real-time H.263 video is presented. By utilizing a feedback channel, the decoder reports the addresses of corrupted blocks induced by transmission errors back to the encoder. With these negative acknowledgments, the encoder can precisely calculate and track the propagated errors by examining the backward motion dependency for each pixel in the current encoding frame. With this precise tracking, the error-propagation effects can be terminated completely by INTRA refreshing the affected macroblocks. In addition, by utilizing the four-corner tracking approximation and the linear motion model, a fast algorithm is also developed to further reduce the computation and memory requirements. The simulations show that both schemes yield significant video quality improvements in error-prone environments. The advantages of the low memory requirement and the low computation complexity are particularly suitable for real-time implementation. RAR 381 êáàéò |
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| Kwong-Keung Leung, Nelson H. C. Yung, and Paul Y. S. Cheung | Parallelization Methodology for Video Coding—An Implementation on the TMS320C80 |
RAR 250 êáàéò |
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| Lorenzo Favalli, Alessandro Mecocci, and Fulvio Moschetti | Object Tracking for Retrieval Applications in MPEG-2 |
Abstract—This paper presents a parallelization methodology for video coding based on the philosophy of hiding as much communications by computation as possible. It models the task/data size, processor cache capacity, and communication contention, through a systematic decomposition and scheduling approach.With the aid of Petri-nets and task graphs for representation and analysis, it employs a triple buffering scheme to enable the functions of frame capture, management, and coding to be performed in parallel. The theoretical speedup analysis indicates that this method offers excellent communication hiding, resulting in system efficiency well above 90%. To prove its practicality, a H.261 video encoder has been implemented on a TMS320C80 system using the method. Its performance was measured, from which the speedup and efficiency figures were calculated. The only difference detected between the theoretical and measured data is the program control overhead that has not been accounted for in the theoretical model. Even with this, the measured speedup of the H.261 is 3.67 and 3.76 on four parallel processors (PPs) for QCIF and 352 240 video, respectively, which correspond to frame rate of 30.7 and 9.25 frames per second, and system efficiency of 91.8% and 94%, respectively. This method is particularly efficient for platforms with small number of parallel processors. RAR 604 êáàéò |
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| Xudong Song, Tihao Chiang, Xiaobing Lee, and Ya-Qin Zhang, Fellow | New Fast Binary Pyramid Motion Estimation for MPEG2 and HDTV Encoding |
Abstract—A novel Fast Binary Pyramid Motion Estimation (FBPME) algorithm is presented in this paper. The proposed FBPME scheme is based on binary multiresolution layers, exclusive- or (XOR) Boolean block matching, and a -scale tiling search scheme. Each video frame is converted into a pyramid structure of 1 binary layers with resolution decimation, plus one integer layer at the lowest resolution. At the lowest resolution layer, the -scale tiling search is performed to select initial motion vector candidates. Motion vector fields are gradually refined with the XOR Boolean block-matching criterion and the -scale tiling search schemes in higher binary layers. FBPME performs several thousands times faster than the conventional full-search block-matching scheme at the same PSNR performance and visual quality. It also dramatically reduces the bus bandwidth and on-chip memory requirement. Moreover, hardware complexity is low due to its binary nature. Fully functional software MPEG-2 MP@ML encoders and Advanced Television Standard Committee High Definition Television encoders based on the FBPME algorithm have been implemented. FBPME Hardware architecture has been developed and is being incorporated into single-chip MPEG encoders. A wide range of video sequences at various resolutions has been tested. The proposed algorithm is also applicable to other digital video compression standards such as H.261, H.263, and MPEG4. RAR 563 êáàéò |
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| Sofia Tsekeridou and Ioannis Pitas | MPEG-2 Error Concealment Based on Block-Matching Principles |
Abstract—The MPEG-2 compression algorithm is very sensitive to channel disturbances due to the use of variable-length coding. A single bit error during transmission leads to noticeable degradation of the decoded sequence quality, in that part or an entire slice information is lost until the next resynchronization point is reached. Error concealment (EC) methods, implemented at the decoder side, present one way of dealing with this problem. An errorconcealment scheme that is based on block-matching principles and spatio-temporal video redundancy is presented in this paper. Spatial information (for the first frame of the sequence or the next scene) or temporal information (for the other frames) is used to reconstruct the corrupted regions. The concealment strategy is embedded in the MPEG-2 decoder model in such a way that error concealment is applied after entire frame decoding. Its performance proves to be satisfactory for packet error rates (PER) ranging from 1% to 10% and for video sequences with different content and motion and surpasses that of other EC methods under study. RAR 1439 êáàéò |
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| Eckhart Baum, Volker Harr, and Joachim Speidel | Improvement of H.263 Encoding by Adaptive Arithmetic Coding |
Abstract—Arithmetic coding in H.263 is based on models that assign a fixed probability to each possible value of some syntax element. In this paper, the effect of adapting the models according to the dynamically changing statistics is analyzed. Simulation results show improvements in all studied cases. RAR 52 êáàéò |
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| Daniel F. Zucker,, Ruby B. Lee, and Michael J. Flynn | Hardware and Software Cache Prefetching Techniques for MPEG Benchmarks |
Abstract—With the popularity of multimedia acceleration instructions such as MMX, MPEG decompression is increasingly executed on general purpose processors instead of dedicated MPEG hardware. The gap between processor speed and memory access means that a significant amount of time is spent in the memory system. As processors get faster—both in terms of higher clock speeds and increased instruction level parallelism—the time spent in the memory system becomes even more significant. Data prefetching is a well-known technique for improving cache performance. While several studies have examined prefetch strategies for scientific and commercial applications, this paper focuses on video applications. Data is presented for three types of hardware-prefetching schemes: the stream buffer, the stride prediction table (SPT), and the stream cache, as well as a new software-directed prefetching technique based on emulation of the hardware SPT. Up to 90% of the misses that would otherwise occur with no prefetching are eliminated. The stream cache can cut execution time by more than half with the addition of a relatively small amount of additional hardware. Software prefetching achieves nearly equal performance with minimal additional hardware. RAR 285 êáàéò |
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| Nikolaos D. Doulamis, Anastasios D. Doulamis, George E. Konstantoulakis, and George I. Stassinopoulos | Efficient Modeling of VBR MPEG-1 Coded Video Sources |
Abstract—Performance evaluation of broadband networks requires statistical analysis and modeling of the actual network traffic. Since multimedia services, and especially variable bit rate (VBR) MPEG-coded video streams are expected to be a major traffic component carried by these networks, modeling of such services and accurate estimation of network resources are crucial for proper network design and congestion-control mechanisms that can guarantee the negotiated quality of service at a minimum cost. The layer modeling of MPEG-1 coded video streams and statistical analysis of their traffic characteristics at each layer is proposed in this paper, along with traffic models capable of estimating the network resources over asynchronous transfer mode (ATM) links. First, based on the properties of the entire MPEG-1 sequence (frame layer signal), a model (Model A) is presented by correlating three stochastic processes in discrete time (autoregressive models), each of which corresponds to the three types of frames of the MPEG encoder ( , and frames). To simplify the traffic Model A and to reduce the required number of parameters, we study the MPEG stream at a higher layer by considering a signal, which expresses the average properties of , and frames over a group of picture (GOP) period. However, models on this layer cannot accurately estimate the network resources, especially in multiplexing schemes. For this reason, an intermediate layer is introduced, which exploits and efficiently combines information of both the aforementioned layers, producing a model (Model B), which requires much smaller number of parameters than Model A and simultaneously provides satisfactory results as far as the network resources are concerned. Evaluation of the validity of the proposed models is performed through experimental studies and computer simulations, using several long duration VBR MPEG-1 coded sequences, different from that used in modeling. The results indicate that both Models A and B are good estimators of video traffic behavior over ATM links at a wide range of utilization. RAR 418 êáàéò |
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| Krit Panusopone, Xuemin Chen, Robert Eifrig, and Ajay Luthra | Coding Tools in MPEG-4 for Interlaced Video |
Abstract—Recent developments in digital video compression, transmission, and displays have made object-based video viable for many applications, e.g., coding chroma-keyed video for digital TV and manipulating video objects on interactive multimedia terminals, etc. To facilitate these applications, there is a demand on international standards for coding methods and transmission formats for object-based natural and synthetic video. For the past few years, the Moving Picture Experts Group (MPEG) of the International Standards Organization (ISO), which successfully created the MPEG-1/2 standards, has beenworking to establish a new standard, called MPEG-4. MPEG-4 will provide standardized technological elements enabling the integration of the production, distribution, and content-access paradigms in four fields: wireless communication, digital TV, interactive graphics, and the World Wide Web. To meet the needs of interlaced video applications, MPEG-4 video adopted interlaced coding tools similar to those in MPEG-2 and features schemes to code multiple video objects. This paper provides an overview of MPEG-4 interlaced coding tools, and focuses in detail on the new shape and texture-coding algorithms for interlaced video. RAR 322 êáàéò |
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| Bo Tao, Bradley W. Dickinson, Fellow, and Heidi A. Peterson | Adaptive Model-Driven Bit Allocation for MPEG Video Coding |
Abstract—We present an adaptive model-driven bit-allocation algorithm for video sequence coding. The algorithm is based on a parametric rate-distortion model, and facilitates both pictureand macroblock-level bit allocation. A region classification scheme is incorporated into the algorithm, which exploits characteristics of human visual perception to efficiently allocate bits according to a region's visual importance. The application of this algorithm to MPEG video coding is discussed in detail. We show that the proposed algorithm is computationally efficient and has many advantages over the MPEG2 TM5 bit-allocation algorithm. RAR 257 êáàéò |
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| Judy Y. Liao and John Villasenor | Adaptive Intra Block Update for Robust Transmission of H.263 |
Abstract—An adaptive block-based intra refresh algorithm for increasing error robustness in an interframe coding system is described. The goal of this algorithm is to allow the intra update rates for different image regions to vary according to various channel conditions and image characteristics. The update scheme is based on an “error-sensitivity metric,” accumulated at the encoder, representing the vulnerability of each coded block to channel errors. As each new frame is encoded, the accumulated metric for each block is examined, and those blocks deemed to have an unacceptably high metric are sent using intra coding as opposed to inter coding. This approach requires no feedback channel and is fully compatible with H.263. It involves a negligible increase in encoder complexity and no change in the decoder complexity. Simulations performed using an H.263 bitstream corrupted by channel errors demonstrate a significant improvement in terms of error recovery time over nonadaptive intra update strategies. RAR 90 êáàéò |
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| Jeff McVeigh, George K. Chen, Judi Goldstein, Atul Gupta, Mike Keith, and Steve Wood | A Software-Based Real-Time MPEG-2 Video Encoder |
Abstract—Dedicated hardware previously has been required to perform real-time MPEG-2 video encoding. However, with increases in clock frequency and the introduction of video-specific instruction sets, general-purpose processors can now approximate the function and performance of single-function hardware. In this paper, we describe a software-only MPEG-2 (MP@ML) video encoder implemented on a personal computer using an Intel™ Pentium® III processor. This encoder is capable of real-time operation while consuming less than 70% of the processor. The main contribution of this work is a set of algorithmic simplifications that significantly reduces the computational load of the encoding process while only slightly degrading the subjective video quality compared to encoders that are more exhaustive. RAR 174 êáàéò |
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| Han Seung Jung, Rin-Chul Kim, and Sang-Uk Lee | A Hierarchical Synchronization Technique Based on the EREC for Robust Transmission of H.263 Bit Stream |
Abstract—In this letter, we propose an error-resilient transmission technique for the H.263 compatible video data stream, based on the data-partitioning technique. The proposed algorithm employs the bit rearrangement technique of the error-resilience entropy coding in each layer, providing unequal error protection against the channel errors, without requiring additional side information. In addition, we propose the recovery algorithm for the lost or erroneous motion vectors. The proposed algorithm is implemented, based on the H.263 standard, and evaluated through intensive computer simulation. The experimental results demonstrate that the proposed algorithm provides acceptable performance both subjectively and objectively at various bit error rates and burst lengths. RAR 190 êáàéò |
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| Jordi Ribas-Corbera and Shaw-Min Lei | A Frame-Layer Bit Allocation for H.263+ |
Abstract—In typical block-based video coding, the rate-control scheme allocates a target number of bits to each frame of a video sequence and selects the block quantization parameters to meet the frame targets. In this work, we present a new technique for assigning such targets. This method has been adopted in the recent test model TMN10 of H.263+, but it is applicable to any video coder and is particularly useful for those that use frames. Our approach selects the frame targets using formulas that result from combining an analytical rate-distortion optimization and a heuristic technique that compensates for the distortion dependency among frames. The method does not require pre-analyses, and encodes each frame only once; hence, it is geared toward low-complexity real-time video coding. We compare this new frame-layer bit allocation in TMN10 to that in MPEG2’s TM5 for a variety of bit rates and video sequences. RAR 120 êáàéò |
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| Jian Zhang, John F. Arnold, and Michael R. Frater | A Cell-Loss Concealment Technique for MPEG-2 Coded Video |
Abstract—Audio-visual and other multimedia services are seen as important sources of traffic for future telecommunication networks, including wireless networks. A major drawback with some wireless networks is that they introduce a significant number of transmission errors into the digital bitstream. For video, such errors can have the effect of degrading the quality of service to the point where it is unusable. In this paper, we introduce a technique that allows for the concealment of the impact of these errors. Our work is based on MPEG-2 encoded video transmitted over a wireless network whose data structures are similar to those of asynchronous transfer mode (ATM) networks. Our simulations include the impact of the MPEG-2 systems layer and cover cell-loss rates up to 5%. This is substantially higher than those that have been discussed in the literature up to this time. We demonstrate that our new approach can significantly increase received video quality, but at the cost of a considerable computational overhead.We then extend our technique to allow for higher computational efficiency and demonstrate that a significant quality improvement is still possible. RAR 286 êáàéò |
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| Fabio Lavagetto and Roberto Pockaj | The Facial Animation Engine: Toward a High-Level Interface for the Desgn of MPEG-4 Compliant Animated Faces |
Abstract—In this paper, we propose a method for implementing a high-level interface for the synthesis and animation of animated virtual faces that is in full compliance with MPEG-4 specifications. This method allows us to implement the simple facial object profile and part of the calibration facial object profile. In fact, starting from a facial wireframe and from a set of con- figuration files, the developed system is capable of automatically generating the animation rules suited for model animation driven by a stream of facial animation parameters. If the calibration parameters (feature points and texture) are available, the system is able to exploit this information for suitably modifying the geometry of the wireframe and for performing its animation by means of calibrated rules computed ex novo on the adapted somatics of the model. RAR 1230 êáàéò |
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| Austin Y. Lan, Anthony G. Nguyen, and Jenq-Neng Hwang | Scene-Context-Dependent Reference-Frame Placement for MPEG Video Coding |
Abstract—The MPEG video-compression standard effectively exploits spatial, temporal, and coding redundancies in the algorithm. In its generic form, however, only a minimal amount of scene adaptation is performed. Video can be further compressed by taking advantage of scenes where the temporal statistics allow larger interreference-frame distances. This paper proposes the use of motion analysis (MA) to adapt to scene content. The actual picture type [intracoded (I), predicted (P), or bidirectionally coded (B)] decision is made by examining the accumulation of motion measurements since the last reference frame (either I or P) was labeled. The proposed MA-based adaptivereference frame-placement scheme outperforms the standard fixed-reference frame-placement and adaptive schemes based on histogram of difference. When compared with the standard fixed scheme, depending on the video contents, this proposed algorithm can achieve from 2 to 13.9% savings in bits while maintaining similar quality. RAR 628 êáàéò |
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| Jos´e I. Ronda, Martina Eckert, Fernando Jaureguizar, and Narciso Garc´ýa | Rate Control and Bit Allocation for MPEG-4 |
Abstract—In recent years, an interest has developed in the coded representations of video signals allowing independent manipulation of semantically independent elements (objects). Along these lines, the ISO standard MPEG-4 enhances the traditional concept of video sequence to convert it into a synchronized set of visual objects organized in a flexible way. The real-time generation of a bitstream according to this new paradigm, and suitable for its transmission through either fixed- or variablerate channels, results in a challenging new bit-allocation and rate-control problem, which has to satisfy complex application requirements. This paper formalizes this new issue by focusing on the design of rate-control systems for real-time applications. The proposed approach relies on the modelization of the source and the optimization of a cost criterion based on signal quality parameters. Different cost criteria are provided, corresponding to a set of relevant definitions of the object priority concept. Algorithms are introduced to minimize the average distortion of the objects, to guarantee desired qualities to the most relevant ones, and to keep constant ratios among the object qualities. RAR 722 êáàéò |
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| Peter Cherriman, Thomas Keller, and Lajos Hanzo | Orthogonal Frequency-Division Multiplex Transmission of H.263 Encoded Video over Highly Frequency-Selective Wireless Networks |
Abstract— The video performance of a 155-Mbps wireless asynchronous transfer mode (WATM) proposal and that of a 2-Mbps Universal Mobile Telecommunications System (UMTS) concept is evaluated for a range of low- to high-quality video application scenarios, various propagation conditions, and video bit rates using the H.263 video codec, assisted by a novel packetization and packet acknowledgment scheme. Orthogonal frequency-division multiplexing is invoked over the highly dispersive channels for conveying high-rate video signals. Various binary Bose–Chaudhuri–Hochquenghem and turbo codes are investigated comparatively, with the conclusion that due to the high error resilience of the video packetization and acknowledgment scheme, the increased power of the higher complexity turbo codec does not translate to substantially improved overall system robustness, although the bit error rate and acknowledgment flag error rate are significantly reduced. The whole range of video resolutions and system parameters is summarized for reasons of space economy in Tables II–IV. The required channel signal-to-noise ratio for near-unimpaired video quality is about 16 dB for the inherently lower quality, lower resolution video frame formats, but slightly higher, about 18 dB, for the high-definition formats, where the error-induced subjective video degradations become more objectionabl over the highly dispersive worst case channels used. RAR 334 êáàéò |
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| Gauthier Lafruit, Lode Nachtergaele, Jan Bormans, Marc Engels, and Ivo Bolsens | Optimal Memory Organization for Scalable Texture Codecs in MPEG-4 |
Abstract— This paper addresses the problem of minimizing memory size and memory accesses in multiresolution texture coding architectures for discrete cosine transform (DCT) and wavelet-based schemes used, for example, in virtual-world walkthroughs or facial animation scenes of an MPEG-4 system. The problem of minimizing the memory cost is important since memory accesses, memory bandwidth limitations, and in general the correct handling of the data flows have become the true critical issues in designing high-speed and low-power video-processing architectures and in efficiently using multimedia processors. For instance, the straightforward implementation of a multiresolution texture codec typically needs an extra memory buffer of the same size as the image to be encoded/decoded. We propose a new calculation schedule that reduces this buffer memory size with up to two orders of magnitude, while still ensuring a number of external (off-chip) memory accesses that is very close to the theoretical minimum. The analysis is generic and is therefore useful for both wavelet and multiresolution DCT codecs. RAR 816 êáàéò |
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| Andr´e Kaup | Object-Based Texture Coding of Moving Video in MPEG-4 |
Abstract—This paper describes some of the most promising segment-based coding techniques which have been investigated in the course of the MPEG-4 standardization process. Padding methods aim at extending arbitrarily shaped image segments to a regular block grid such that common hybrid block-based coding techniques can be applied. A simple and efficient padding technique employing low-pass extrapolation is outlined which yields a signal extension with high energy concentration in the low-frequency area. Simulations indicate that this method is well suited for block-based video coding, and clearly outperforms other low-complexity extrapolation methods with respect to coding efficiency. In contrast to padding techniques, shape-adaptive methods take advantage of the shape information available at the decoder side. A well-known representative of this class is the SA–DCT. However, having been primarily designed for intraframe coding, it is shown that the transform is suboptimal when applied to interframe coding. Using a suitable covariance model, it is demonstrated that a rescaled, orthonormalized transform much closer approximates the optimal shape-adaptive eigentransform of motion-compensated frame difference images. Rate distortion curves verify that orthonormalization improves coding efficiency in interframe coding by up to 2 dB while not adding to complexity. In a comparison, it is finally shown that extrapolation and SA–DCT perform very closely in the case of low data rates, while there is a clear advantage for the shape-adaptive transform in the case of high-quality video coding. RAR 312 êáàéò |
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| Noel Brady | MPEG-4 Standardized Methods for the Compression of Arbitrarily Shaped Video Objects |
Abstract—MPEG-4 is the most recent standard for audio-visual representation to be published by the International Organization for Standardization. One of the many new features of MPEG-4 is its ability to represent two-dimensional video objects of arbitrary shape. For this purpose, MPEG-4 uses the conventional motioncompensated discrete cosine transform syntax for color/texture coding and augments this with an explicit compressed representation of the video object’s shape. This paper is intended as a tutorial in the means of encoding and decoding arbitrarily shaped video objects as specified by MPEG-4. The major emphasis of the paper is on explaining the compression technology associated with the normative shape representation, i.e., block-based contextbased arithmetic encoding, but some new aspects associated with arbitrarily shaped texture coding are also highlighted. The MPEG-4 specifications are presented in an informal way, and the motivations underlying the algorithm are clarified. In addition, effective methods are suggested for performing many of the nonnormative encoding tasks, and several encoding performance tradeoffs are illustrated. RAR 580 êáàéò |
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| Anthony Vetro, Huifang Sun, and Yao Wang | MPEG-4 Rate Control for Multiple Video Objects |
Abstract—This paper describes an algorithm which can achieve a constant bit rate when coding multiple video objects. The implementation is a nontrivial extension of the MPEG-4 rate control algorithm for single video objects which employs a quadratic ratequantizer model. The algorithm is organized into two stages: a pre- and a postencoding stage. In the preencoding stage, an initial target estimate is made for each object. Based on the buffer fullness, the total target is adjusted and then distributed proportional to the relative size, motion, and variance of each object. Based on the new individual targets and rate-quantizer relation for texture, appropriate quantization parameters are calculated. After each object is encoded, the model parameters for each object are updated, and if necessary, frames are skipped to ensure that the buffer does not overflow. A preframeskip control is exercised to avoid buffer overflow when the motion and shape information occupies a significant portion of the bit budget. The rate control algorithm switches between two operation modes so that the coder can reduce the spatial coding accuracy for an improved temporal resolution. A shape-coding control mechanism is also proposed, which provides a tradeoff between texture and shape coding accuracy. Overall, the algorithm is able to successfully achieve the target bit rate, effectively code arbitrarily shaped objects, and maintain a stable buffer level. These techniques have been adopted by the MPEG committee in July 1997 as part of the video Verification Model (VM8). RAR 484 êáàéò |
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| Gabriel Antunes Abrantes, and Fernando Pereira | MPEG-4 Facial Animation Technology: Survey, Implementation, and Results |
Abstract—The emerging MPEG-4 standard specifies an objectbased audiovisual representation framework, integrating both natural and synthetic content. Tools supporting three-dimensional facial animation will be standardized for the first time. To support facial animation decoders with different degrees of complexity, MPEG-4 uses a profiling strategy, which foresees the specification of object types, profiles, and levels adequate to the various relevant application classes. This paper first gives an overview of the MPEG-4 facial animation technology. Subsequently, the paper describes the Instituto Superior T´ecnico implementation of an MPEG-4 facial animation system, then briefly evaluates the performance of the various tools standardized, using the MPEG-4 test material. RAR 1153 êáàéò |
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| Junehwa Song, and Boon-Lock Yeo | Fast Extraction of Spatially Reduced Image Sequences from MPEG-2 Compressed Video |
Abstract—MPEG-2 video standards are targeted for highquality video broadcast and distribution and are optimized for efficient storage and transmission. However, it is difficult to process MPEG-2 for video browsing and database applications without first decompressing the video. Yeo and Liu [1] have proposed fast algorithms for the direct extraction of spatially reduced images from MPEG-1 video. Reduced images have been demonstrated to be effective for shot detection, shot browsing and editing, and temporal processing of video for video presentation and content annotation. In this paper, we develop new tools to handle the extra complexity in MPEG-2 video for extracting spatially reduced images. In particular, we propose new classes of discrete cosine transform (DCT) domain and DCT inverse motion compensation operations for handling the interlaced modes in the different frame types of MPEG-2, and we design new and efficient algorithms for generating spatially reduced images of an MPEG- 2 video. The algorithms proposed in this paper are fundamental for efficient and effective processing of MPEG-2 video. RAR 767 êáàéò |
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| Carsten Herpel | Elementary Stream Management in MPEG-4 |
Abstract—The forthcoming MPEG-4 standard specifies in its systems part an audiovisual scene description and functionality for the elementary stream management. The elementary streammanagement functionality is introduced here. It consists of a media object description framework that describes the streaming resources that form part of an MPEG-4 presentation and of a synchronization syntax incorporated in a flexible sync layer with an underlying systems decoder model. The final section outlines the transport and session setup for MPEG-4 presentations on relevant transport media, namely, the Internet and in digital broadcast scenarios. RAR 338 êáàéò |
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| Han-Chiang Shyu and Jin-Jang Leou | Detection and Concealment of Transmission Errors in MPEG-2 Images—A Genetic Algorithm Approach |
Abstract—In this paper, the detection and concealment approach to transmission errors in MPEG-2 images using genetic algorithms (GA’s) is proposed. For entropy-coded MPEG-2 images, a transmission error in a codeword will not only affect the underlying codeword but also may affect subsequent codewords, resulting in a great degradation of the received images. Here, a transmission error may be a single-bit error or a burst error. The objective of the proposed approach is to recover high-quality MPEG-2 images from the corresponding corrupted MPEG-2 images without increasing the transmission bit rate. In the proposed error-detection approach, by using the constraints imposed on compressed image data, all the slices within an MPEG-2 picture can be correctly located. After a slice is located, similar to Chu and Leou [22], transmission errors within the slice are detected by two successive procedures: 1) whether the slice is corrupted or not is determined by checking a set of error-detection conditions under decoding and 2) the precise location (block-based) of the first transmission error (i.e., the first corrupted block) within the corrupted slice is located by a block-based backtracking procedure. For a corrupted block, the proposed GA approach to error concealment is employed to conceal the corrupted block by iteratively performing reproduction/ crossover/mutation operations and evaluating the proposed fitness function until the stopping criterion is satisfied. Based on the simulation results obtained in this study, the proposed approach can recover high-quality MPEG-2 images from the corresponding corrupted images up to a bit error rate of 0.5%. RAR 1324 êáàéò |
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| Hai Tao, Homer H. Chen, Wei Wu, and Thomas S. Huang, Fellow | Compression of MPEG-4 Facial Animation Parameters for Transmission of Talking Heads |
Abstract—The emerging MPEG-4 standard supports the transmission and composition of facial animation with natural video. The new standard will include a facial animation parameter (FAP) set that is defined based on the study of minimal facial actions and is closely related to muscle actions. The FAP set enables model-based representation of natural or synthetic talking-head sequences and allows intelligible visual reproduction of facial expressions, emotions, and speech pronunciations at the receiver. This paper addresses the data-compression issue of talking heads and presents three methods for bit-rate reduction of FAP’s. Compression efficiency is achieved by way of transform coding, principal component analysis, and FAP interpolation. These methods are independent of each other in nature and thus can be applied in combination to lower the bit-rate demand of FAP’s, making possible the transmission of multiple talking heads over band-limited channels. The basic methods described here have been adopted into the MPEG-4 Visual Committee Draft [1] and are readily applicable to other articulation data such as body animation parameters. The efficacy of the methods is demonstrated by both subjective and objective results. RAR 652 êáàéò |
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| Jui-Hua Li and Nam Ling | Architecture and Bus-Arbitration Schemes for MPEG-2 Video Decoder |
Abstract—An efficient MPEG-2 video decoder architecture together with several effective bus-arbitration schemes designed to meet the main profile at main level (MP@ML) real-time decoding requirement is presented in this paper. The overall architecture, as well as the design of major function-specific processing blocks (variable-length decoder, inverse two-dimensional discrete cosine transform unit, and motion-compensation unit), is discussed. A hierarchical and distributed controller approach is used, a bus-monitoring model for different bus-arbitration schemes to control external DRAM accesses is developed, and the system is simulated. Practical issues and buffer sizes are addressed and evaluated. With a 27-MHz clock, our architecture uses many fewer than the 667 cycles, the upper bound for the MP@ML decoding requirement, to decode each macroblock with a single external bus and DRAM. RAR 549 êáàéò |
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| JPaul G. Howard, Faouzi Kossentini, Bo Martins, Søren Forchhammer, and William J. Rucklidge | The Emerging JBIG2 Standard |
Abstract—The Joint Bi-Level Image Experts Group (JBIG), an international study group affiliated with ISO/IEC and ITU-T, is in the process of drafting a new standard for lossy and lossless compression of bilevel images. The new standard, informally referred to as JBIG2, will support model-based coding for text and halftones to permit compression ratios up to three times those of existing standards for lossless compression. JBIG2 will also permit lossy preprocessing without specifying how it is to be done. In this case, compression ratios up to eight times those of existing standards may be obtained with imperceptible loss of quality. It is expected that JBIG2 will become an international standard by 2000. RAR 685 êáàéò |
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| Peter Cherriman and Lajos Hanzo | Programmable H.263-Based Wireless Video Transceivers for Interference-Limited Environments |
Abstract— In order to exploit the nonuniformly distributed channel capacity over the cell area, the intelligent 7.3-kB programmable videophone transceiver of Table I is proposed, which is capable of exploiting the higher channel capacity of uninterfered, high-channel-quality cell areas, while supporting more robust, but lower bit-rate operation in more interfered areas. The system employed an enhanced H.263-compatible video codec. Since most existing wireless systems exhibit a constant bit-rate, the video codec’s bit-rate fluctuation was smoothed by a novel adaptive packetization algorithm, which is capable of supporting automatic repeat request (ARQ)-assisted operation in wireless distributive video transmissions, although in the proposed lowlatency interactive videophone transceiver, we refrained from using ARQ. Instead, corrupted packets are dropped by both the local and remote decoders in order to prevent error propagation. The minimum required channel signal-to-interference-plus-noise ratio (SINR) was in the range of 8–28 dB for the various transmission scenarios of Table I, while the corresponding video peak-signal-to-noise ratio (PSNR) was in the range of 32–39 dB. The main system features are summarized in Table I. RAR 288 êáàéò |
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| Guy Cˆot´e, Berna Erol, Michael Gallant, and Faouzi Kossentini | H.263+: Video Coding at Low Bit Rates |
Abstract—In this tutorial paper, we discuss the ITU-T H.263+ (or H.263 Version 2) low-bit-rate video coding standard. We first describe, briefly, the H.263 standard including its optional modes. We then address the 12 new negotiable modes of H.263+. Next, we present experimental results for these modes, based on our public-domain implementation (see our Web site at http://spmg.ece.ubc.ca). Tradeoffs among compression performance, complexity, and memory requirements for the H.263+ optional modes are discussed. Finally, results for mode combinations are presented. RAR 667 êáàéò |
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| Yao Wang and J¨orn Ostermann | Evaluation of Mesh-Based Motion Estimation in H.263-Like Coders |
Abstract—In this paper, we present two mesh-based motion estimation algorithms, and evaluate their performance when incorporated in an H.263-like block-based video coder. Both algorithms compute nodal motions in a hierarchical manner. Within each hierarchy level, the first algorithm (HMMA) minimizes the prediction error in the four elements surrounding each node, where the prediction is accomplished by a bilinear mapping. The optimal solution is obtained by a full search within a range defined by the topology of the mesh. The second algorithm (HBMA) minimizes the error in a block surrounding each node, assuming the motion in the block is constant. In both cases, bilinear mapping is used for motion-compensated prediction based on nodal displacements. The two algorithms are compared with an exhaustive block-matching algorithm (EBMA) by evaluating their performances in temporal prediction and in an H.263/TMN4 coder. For prediction only, the HMMA and HBMA algorithms yield visually more satisfactory results, even though the PSNR’s of predicted images are on average lower. The coded images also have lower PSNR’s at similar bit rates. The coding artifacts are different: while the block-based method leads to more severe block distortions, the mesh-based method experiences some warping artifacts. The HMMA algorithm outperforms HBMA slightly for certain sequences at the expense of higher computational complexity. RAR 233 êáàéò |
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| Stephan Wenger, Gerd Knorr, J¨org Ott, and Faouzi Kossentini | Error Resilience Support in H.263+ |
Abstract—Version 2 of ITU Recommendation H.263, better known as H.263+, includes a number of new mechanisms to improve coding efficiency and support various types of networks more efficiently. This paper provides an overview of the error resilience optional modes of H.263+ and describes the use of such modes in various network scenarios. RAR 202 êáàéò |
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| Wenwu Zhu, Yiwei Thomas Hou, Yao Wang, and Ya-Qin Zhang | End-to-End Modeling and Simulation of MPEG-2 Transport Streams over ATM Networks with Jitter |
Abstract—In this paper, the operation of MPEG-2 systems is modeled and simulated when an MPEG-2 transport stream is delivered through an ATM network with jitter. End-to-end packet-based analysis is performed for delivery of MPEG-2 transport streams over ATM networks. A novel approach to analyzing the decoder buffer behavior in the presence of network jitter is presented. The probability density function of the interarrival time of the ATM adaptation layer 5 (AAL5) protocol data unit (PDU) is derived from an MPEG-2 video source model and an ATM network jitter model. Based on a real-time decoding requirement of the MPEG-2 transport stream (TS) system target decoder (T-STD), the decoder buffer behavior is simulated. In this simulation, the packets’ arrivals follow the derived probability density function of the AAL5 PDU interarrival time. The modeling and simulation results show the interactions among packet loss ratio, decoder buffer size, and network jitter level. We found that jitter affects decoder buffer size and packet loss ratio in a significant way. RAR 70 êáàéò |
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| Wen-Jeng Chu and Jin-Jang Leou | Detection and Concealment of Transmission Errors in H.261 Images |
Abstract—In this study, the detection and concealment approach to transmission errors in H.261 images is proposed. For entropy-coded H.261 images, a transmission error in a codeword will not only affect the underlying codeword, but also may affect subsequent codewords, resulting in a great degradation of the received images. Here a transmission error may be a single-bit error or a burst error containing N successive error bits. The objective of the proposed approach is to recover high-quality H.261 images from the corresponding corrupted H.261 images, without increasing the transmission bit rate. In the proposed approach, using the constraints imposed on compressed image data, all the groups of blocks (GOB’s) within an H.261 picture can be correctly located. After a GOB is located, transmission errors within the GOB are detected by two successive procedures: 1) whether the GOB is corrupted or not is determined by checking a set of error-checking conditions under decoding and 2) the precise location (block-based) of the first transmission error (i.e., the first corrupted block) within the GOB is located by a block-based backtracking procedure. For a corrupted block, a set of concealed block candidates, SC, is generated, and a proposed fitness function for error concealment is used to select the “best” concealed block candidate among SC as the concealed block of the corrupted block. Based on the simulation results obtained in this study, the proposed approach can indeed recover high-quality H.261 images from their corresponding corrupted H.261 images. This shows the feasibility of the proposed approach. RAR 295 êáàéò |
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| Yong He, Ishfaq Ahmad, and Ming L. Liou, Fellow | A Software-Based MPEG-4 Video Encoder Using Parallel Processing |
Abstract—In this paper, we describe a software-based MPEG- 4 video encoder which is implemented using parallel processing on a cluster of workstations collectively working as a virtual machine. The contributions of our work are as follows. First, a hierarchical Petri-nets-based modeling methodology is proposed to capture the spatiotemporal relationships among multiple objects at different levels of an MPEG-4 video sequence. Second, a scheduling algorithm is proposed to assign video objects to workstations for encoding in parallel. The algorithm determines the execution order of video objects, ensures that the synchronization requirements among them are enforced and that presentation deadlines are met. Third, a dynamic partitioning scheme is proposed which divides an object among multiple workstations to extract additional parallelism. The scheme achieves load balancing among the workstations with a low overhead. The striking feature of our encoder is that it adjusts the allocation and partitioning of objects automatically according to the dynamic variations in the video object behavior. We have made various additional software optimizations to further speed up the computation. The performance of the encoder can scale according to the number of workstations used. With 20 workstations, the encoder yields an encoding rate higher than real time, allowing the encoding of multiple sequences simultaneously. RAR 534 êáàéò |
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| Pedro A. A. Assun¸c˜ao and Mohammed Ghanbari | A Frequency-Domain Video Transcoder for Dynamic Bit-Rate Reduction of MPEG-2 Bit Streams |
Abstract—Many of the forthcoming video services and multimedia applications are expected to use preencoded video for storage and transmission. Video transcoding is intended to provide transmission flexibility to preencoded bit streams by dynamically adjusting the bit rate of these bit streams according to new bandwidth constraints that were unknown at the time of encoding. In this paper, we propose a drift-free MPEG-2 video transcoder, working entirely in the frequency domain. The various modes of motion compensation (MC) defined in MPEG-2 are implemented in the discrete cosine transform (DCT) domain at reduced computational complexity. By using approximate matrices to compute the MC–DCT blocks, we show that computational complexity can be reduced by 81% compared with the pixel domain approach. Moreover, by using a Lagrangian rate-distortion optimization for bit reallocation, we show that optimal transcoding of high-quality bit streams can produce better picture quality than that obtained by directly encoding the uncompressed video at the same bit rates using a nonoptimized Test Model 5 (TM5) encoder. RAR 464 êáàéò |
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| Thomas Sikora | The MPEG-4 Video Standard Verification Model |
Abstract—The MPEG-4 standardization phase has the mandate to develop algorithms for audio-visual coding allowing for interactivity, high compression, and/or universal accessibility and portability of audio and video content. In addition to the conventional “frame”-based functionalities of the MPEG-1 and MPEG-2 standards, the MPEG-4 video coding algorithm will also support access and manipulation of “objects” within video scenes. The January 1996 MPEG Video group meeting witnessed the definition of the first version of the MPEG-4 Video Verification Model—a milestone in the development of the MPEG-4 standard. The primary intent of the Video Verification Model is to provide a fully defined core video coding algorithm platform for the development of the standard. As such, the structure of the MPEG-4 Video Verification Model already gives some indication about the tools and algorithms that will be provided by the final MPEG-4 standard. The purpose of this paper is to describe the scope of the MPEG-4 Video standard and to outline the structure of the MPEG-4 Video Verification Model under development. Index Terms— Coding efficiency, compression, error robustness, flexible coding, functional coding, manipulation, MPEG, MPEG-4, multimedia, natural video, object-based coding, SNHC, standardization, synthetic video, universal accessibility, verification model, video coding. RAR 1042 êáàéò |
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| Jungwoo Lee, and Bradley W. Dickinson, Fellow | Rate-Distortion Optimized Frame Type Selection for MPEG Encoding |
Abstract—In this paper, we present an algorithm for joint optimization of anchor frame separation and bit allocation for motion-compensated video coders. The anchor frame separation is optimized in the sense that the distortion is minimized under a bit budget constraint. At the same time, the quantization for each frame in a group of pictures is also optimized in an operational rate distortion sense. The optimal anchor frame separation does depend on the quantization of each frame so that the two optimization problems cannot be separated. A Lagrange multiplier approach can be used to obtain the optimal solution if we assume that the rate-distortion curve is convex. Heuristic algorithms based on simulated annealing and greedy trellis selection are also presented to reduce the computational complexity. RAR 289 êáàéò |
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| Fernando Pereira, and Thierry Alpert | MPEG-4 Video Subjective Test Procedures and Results |
Abstract—In the recent years, the technical developments in the area of audio-visual communications, notably in video coding, encouraged the emergence of new services which are already changing our everyday life. The convergence of the telecommunications, computer, and TV/film technologies is leading to the intermixture of elements formerly characteristic of each one of these fields, creating new needs and new requirements. Among the most important trends is the need to increase the interaction capabilities between the user and the audio-visual information, notably by considering the scene as a composition of objects—the content—according to a script that describes their spatial and temporal behavior and not just a set of pixels. MPEG-4 is a new audio-visual standard aiming to establish a universal, efficient coding of different forms of audio-visual data, called audio-visual objects. To reach this target, MPEG-4 has called for proposals on techniques that may be instrumental to efficiently represent visual information, allowing simultaneously high degrees of content-based interactivity and error resilience. This paper addresses the conditions under which the proposals to the MPEG-4 first round of video subjective tests have been evaluated. Moreover, the most significative results of these tests are also presented. RAR 607 êáàéò |
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| Huifang Sun, Wilson Kwok, Max Chien, and C. H. John Ju | MPEG Coding Performance Improvement by Jointly Optimizing Coding Mode Decisions and Rate Control |
Abstract—This paper presents a new algorithm for determining the optimal MPEG [1] coding strategy in terms of the selection of macroblock coding modes and quantizer scales. In the algorithm proposed in the Test Model [2] the rate control operates independently from the coding mode selection for each macroblock. The coding mode is decided based only upon the energy of predictive residues. Actually, the two processes of coding mode decision and rate control are intimately related to each other and should be determined jointly in order to achieve optimal coding performance. We formulate the constrained optimization problem and present solutions based upon rate-distortion characteristics, or R(D) curves, for all the macroblocks that compose the picture being coded. Distortion for the entire picture is assumed to be decomposable and expressible as a function of individual macroblock distortions, with this being the objective function to minimize. The determination of the optimal solution is complicated by the MPEG differential encoding of motion vectors and dc coefficients, which introduce dependencies that carry over from macroblock to macroblock for a duration equal to the slice length. As an approximation, a near-optimum greedy algorithm is proposed. Once the upper bound in performance is calculated, it can be used to assess how well practical suboptimum methods perform. Finally, such a practical suboptimum algorithm is proposed and evaluated. RAR 291 êáàéò |
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| Leonardo Chiariglione | MPEG and Multimedia Communications |
Abstract—Digital television is a reality today, but multimedia communications, after years of hype, is still a catchword. Lack of suitable multi-industry standards supporting it is one reason for the unfulfilled promise. The MPEG committee which originated the MPEG-1 and MPEG-2 standards that made digital television possible is currently developing MPEG-4 with wide industry participation. This paper describes how the MPEG-4 standard, with its networkindependent nature and application-level features, is poised to become the enabling technology for multimedia communications and will therefore contribute to solve the problems that are hindering multimedia communications. RAR 189 êáàéò |
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| C. Michael Sharon, Ioannis Lambadaris, Michael Devetsikiotis,and A. Roger Kaye | Modeling and Control of VBR H.261 Video Transmission over Frame Relay Networks |
Abstract—This paper examines the transmission of variable bitrate (VBR) H.261 video traffic over a mixed traffic (video/inter- LAN data) integrated services frame relay (FR) network. We introduce a modified H.261 codec that produces VBR output and show that parsing of the video bit stream at group of blocks (GOB) boundaries produces variable length FR packets which are well suited to network characteristics.We demonstrate that GOBlevel video traffic requires a more sophisticated statistical model of the resulting data stream than the frame-level models that are frequently used. The transform expand sample (TES) technique is used to obtain an accurate model of the autocorrelation and the marginal probability distribution of the bit-rate variations at the GOB level. A simple and effective methodology is introduced for capturing the periodic components that are present in the GOBlevel autocorrelation. The methodology is extended to permit simulations of VBR codecs in which the codec quantization step size is adjusted in response to prevailing network conditions. Furthermore, we show that the quality of service requirements of VBR video can be met in the presence of inter-LAN data traffic by making use of the FR backward explicit congestion notification (BECN) facility in conjunction with a modified H.261 codec whose rate is controlled by the congestion notification. We also show that the performance of the control mechanism is significantly influenced by a subset of network threshold and codec control parameters which are identified using 2k factorial analysis techniques. Further, we obtain optimal ranges of values for these parameters using mean field annealing. Finally, we show that variable quantization rate control may be more effective for this purpose than variable frame rate control, and that the resulting improvement in performance over that of an uncontrolled network can be significant. need for enterprise networks to make flexible use of bandwidth and to explore the potential of packet-switched and frame relay (FR) transport protocols in order to achieve this goal. RAR 234 êáàéò |
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