1,511 research outputs found
Motion Scalability for Video Coding with Flexible Spatio-Temporal Decompositions
PhDThe research presented in this thesis aims to extend the scalability range of the
wavelet-based video coding systems in order to achieve fully scalable coding with a
wide range of available decoding points. Since the temporal redundancy regularly
comprises the main portion of the global video sequence redundancy, the techniques
that can be generally termed motion decorrelation techniques have a central role in
the overall compression performance. For this reason the scalable motion modelling
and coding are of utmost importance, and specifically, in this thesis possible
solutions are identified and analysed.
The main contributions of the presented research are grouped into two
interrelated and complementary topics. Firstly a flexible motion model with rateoptimised
estimation technique is introduced. The proposed motion model is based
on tree structures and allows high adaptability needed for layered motion coding. The
flexible structure for motion compensation allows for optimisation at different stages
of the adaptive spatio-temporal decomposition, which is crucial for scalable coding
that targets decoding on different resolutions. By utilising an adaptive choice of
wavelet filterbank, the model enables high compression based on efficient mode
selection. Secondly, solutions for scalable motion modelling and coding are
developed. These solutions are based on precision limiting of motion vectors and
creation of a layered motion structure that describes hierarchically coded motion.
The solution based on precision limiting relies on layered bit-plane coding of motion
vector values. The second solution builds on recently established techniques that
impose scalability on a motion structure. The new approach is based on two major
improvements: the evaluation of distortion in temporal Subbands and motion search
in temporal subbands that finds the optimal motion vectors for layered motion
structure.
Exhaustive tests on the rate-distortion performance in demanding scalable video
coding scenarios show benefits of application of both developed flexible motion
model and various solutions for scalable motion coding
Quality of Experience and Adaptation Techniques for Multimedia Communications
The widespread use of multimedia services on the World Wide Web and the advances
in end-user portable devices have recently increased the user demands for better quality.
Moreover, providing these services seamlessly and ubiquitously on wireless networks and
with user mobility poses hard challenges. To meet these challenges and fulfill the end-user
requirements, suitable strategies need to be adopted at both application level and network
level. At the application level rate and quality have to be adapted to time-varying bandwidth
limitations, whereas on the network side a mechanism for efficient use of the network
resources has to be implemented, to provide a better end-user Quality of Experience (QoE)
through better Quality of Service (QoS). The work in this thesis addresses these issues by
first investigating multi-stream rate adaptation techniques for Scalable Video Coding (SVC)
applications aimed at a fair provision of QoE to end-users. Rate Distortion (R-D) models
for real-time and non real-time video streaming have been proposed and a rate adaptation
technique is also developed to minimize with fairness the distortion of multiple videos
with difference complexities. To provide resiliency against errors, the effect of Unequal
Error protection (UXP) based on Reed Solomon (RS) encoding with erasure correction has
been also included in the proposed R-D modelling. Moreover, to improve the support of
QoE at the network level for multimedia applications sensitive to delays, jitters and packet
drops, a technique to prioritise different traffic flows using specific QoS classes within an
intermediate DiffServ network integrated with a WiMAX access system is investigated.
Simulations were performed to test the network under different congestion scenarios
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