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Английские материалы
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Название статьи |
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| Seungyup Paek and Shih-Fu Chang |
Video-Server Retrieval Scheduling and Resource
Reservation for Variable Bit Rate Scalable Video |
Abstract—State-of-the-art digital video compression produces
bursty, variable bit rate video. The bursty nature of compressed
video raises challenges in the design of video servers. In this paper,
we first present a method for the efficient retrieval of bursty
video data from the disk system to the memory of a digital video
server. For a single video stream, the proposed retrieval schedule
minimizes the buffer requirement for continuous retrieval, given
that a fixed disk bandwidth is reserved for the entire duration of
retrieval. Secondly, we present an optimal resource-reservation
algorithm for multiple video streams based on the proposed
retrieval schedule. The resource-reservation algorithm maximizes
the number of bursty video streams that can be supported by a
video server, given any disk bandwidth and memory resource.
Thirdly, we present a progressive display scheme for scalable video
that is based on the retrieval schedule and resource-reservation
algorithm. Performance evaluations based on simulations using
MPEG-2 trace data are presented. For a personal computer with
four disks and a memory resource of 120 MB, our approach can
support 50%–275% more video streams than previously proposed
approaches, depending on the pre-fetch delay that users are
willing to tolerate in interactive viewing of videos.
RAR 228 кбайт
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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
RAR 568 кбайт
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| Lilla Bцrцczky, Agnes Y. Ngai, and Edward F. Westermann |
Joint Rate Control with Look-Ahead for
Multi-Program Video Coding |
Abstract—In this paper, we present a new joint rate control
algorithm for a multi-program video compression system using
MPEG-2 compatible video encoders. The proposed joint rate control
is based on both the feedback and look-ahead approaches.
It dynamically distributes the channel bandwidth among the program
encoders according to the relative complexities of the programs
using picture and coding statistics. As opposed to previous
works in this area, our algorithm does not restrict the encoders to
operate with identical group of pictures (GOP) structures, i.e. the
GOP boundaries need not be synchronized among the different encoders.
The proposed algorithm allows adaptive distribution of the
channel bandwidth among the programs, even at the start of encoding.
Furthermore, it assures quick reaction to scene changes,
where a feedback approach requires an unavoidable delay. Experimental
results show that the proposed joint rate control with
look-ahead results in improved picture quality in comparison with
a pure feedback approach.
RAR 120 кбайт
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| Jordi Ribas-Corbera, and Shawmin Lei |
JRate Control in DCT Video Coding
for Low-Delay Communications |
Abstract—An important motivation for the development of the
emerging H.263+ and MPEG4 coding standards is to enhance
the quality of highly compressed video for two-way, real-time
communications. In these applications, the delay produced by bits
accumulated in the encoder buffer must be very small, typically
below 100 ms, and the rate control strategy is responsible for
encoding the video with high quality and maintaining a low
buffer delay. In this work, we present a simple rate control
technique that achieves these two objectives by smartly selecting
the values of the quantization parameters in typical discrete
cosine transform video coders. To do this, we derive models
for bit rate and distortion in this type of coders, in terms of
the quantization parameters. Using Lagrange optimization, we
minimize distortion subject to the target bit constraint, and
obtain formulas that indicate how to choose the quantization
parameters. We implement our technique in H.263 and MPEG4
coders, and compare its performance to TMN7 and VM7 rate
control when the encoder buffer is small, for a variety of video
sequences and bit rates. This new method has recently been
adopted as a rate control tool in the test model TMN8 of H.263+
and (with some modifications) in the verification model VM8 of
MPEG4.
RAR 492 кбайт
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| Josґe I. Ronda, Martina Eckert, Fernando Jaureguizar, and Narciso Garcґэa |
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.
The techniques have been applied to a coder implementing the
MPEG-4 video verification model, showing good properties in
terms of achievement of the control objectives.
RAR 722 кбайт
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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 кбайт
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| Liang-Jin Lin, and Antonio Ortega |
Bit-Rate Control Using Piecewise
Approximated Rate–Distortion Characteristics |
Abstract—Digital video’s increased popularity has been driven
to a large extent by a flurry of recently proposed international
standards (MPEG-1, MPEG-2, H.263, etc.). In most standards,
the rate control scheme, which plays an important role in improving
and stabilizing the decoding and playback quality, is not
defined, and thus different strategies can be implemented in each
encoder design. Several rate–distortion (R–D)-based techniques
have been proposed to aim at the best possible quality for a
given channel rate and buffer size. These approaches are complex
because they require the R–D characteristics of the input data to
be measured before making quantization assignment decisions.
In this paper, we show how the complexity of computing the
R–D data can be reduced without significantly reducing the
performance of the optimization procedure. We propose two
methods which provide successive reductions in complexity by: 1)
using models to interpolate the rate and distortion characteristics,
and 2) using past frames instead of current ones to determine
the models. Our first method is applicable to situations (e.g.,
broadcast video) where a long encoding delay is possible, while
our second approach is more useful for computation-constrained
interactive video applications. The first method can also be used
to benchmark other approaches. Both methods can achieve over
1 dB peak signal-to-noise rate (PSNR) gain over simple methods
like the MPEG Test Model 5 (TM5) rate control, with even
greater gains during scene change transitions. In addition, both
methods make few a priori assumptions and provide robustness
in their performance over a range of video sources and encoding
rates. In terms of complexity, our first algorithm roughly doubles
the encoding time as compared to simpler techniques (such
as TM5). However, complexity is greatly reduced as compared
to methods which exactly measure the R–D data. Our second
algorithm has a complexity marginally higher than TM5 and a
PSNR performance slightly lower than that of the first approach.
RAR 429 кбайт
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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 кбайт
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| Tihao Chiang and Ya-Qin Zhang |
A New Rate Control Scheme Using Quadratic Rate Distortion Model |
Abstract—A new rate control scheme is used to calculate the target
bit rate for each frame based on a quadratic formulation of the rate
distortion function. The distortion measure is assumed to be the average
quantization scale of a frame. The rate distortion function is modeled
as a second-order function of the inverse of the distortion measure.
We presented a closed form solution for the target bit allocation which
includes the MPEG-2 TM5 rate control scheme as a special case. Model
parameters are estimated using statistical linear regression analysis. Since
the estimation uses the past encoded frames of the same picture prediction
type (I; P; B pictures), the proposed approach is a single pass rate
control technique. Because of the improved accuracy of the rate distortion
function, the fluctuations of the bit counts are significantly reduced by
20–65% in standard deviation of the bit count while the picture quality
remains the same. Thus, the buffer requirement is reduced at a small
increase in complexity. This technique has bee adopted by the MPEG
committee as part of VM5.0 in November 1996.
RAR 157 кбайт
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