Английские материалы
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| Авторы |
Название статьи |
Описание |
Рейтинг |
| 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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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| Pedro A. A. Assunзгo 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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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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 кбайт
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