Distributed SIP conference management with autonomously authenticated sources and its application to an H.264 videoconferencing software for mobiles

The design of conferencing systems for achieving efficient and flexible communication in a fully distributed, infrastructure-independent fashion is a promising direction, both in terms of research and practical development. In the particular case of video communication, the seamless adaptation to heterogeneous mobile devices poses an additional strong challenge to those seeking for interoperable and easy-to-deploy solutions. In this paper, we make several contributions towards a generic peer-to-peer (P2P) videoconferencing solution that extends into the mobile realm. We describe the essential building blocks for conference management and media distribution that are necessary for a distributed conferencing approach. Establishing a distributed SIP conference focus, participants share the conference according to their individually given capabilities and resources in terms of bandwidth and processing power rather than in a centralized and fixed way. Overall concepts and SIP-primitives for such an autonomous organization are presented. Security issues that derive from this decentralized identity management are resolved by so-called Overlay AuthoCast, a novel use of cryptographically generated identifiers. Furthermore, this work is dedicated to the development of a software-based H.264 video codec implementation and the specific aspects resulting from tuning such a highly resource-intensive software codec to the given target platform of a standard consumer smartphone.     

Kinetic excitation of solids induced by energetic particle bombardment: Influence of impact angle

The kinetic excitation of a solid surface under bombardment with energetic particles is studied via internal electron emission in a metal-insulator-metal junction. In particular, the dependence of the measured tunneling yield on the projectile impact angle is studied. The resulting impact angle distribution is compared with predictions of the total excitation energy profile calculated using the SRIM 2006 Monte Carlo program package. While the calculated profiles fail to explain the experimental data, it is shown that a simple calculation of impact angle dependent projectile backscattering qualitatively reproduces the observed trends.     

Complexity-constrained best-basis wavelet packet algorithm forimage compression

The concept of adapted waveform analysis using a best-basis selection out of a predefined library of wavelet packet (WP) bases allows an efficient image representation for the purpose of compression. Image coding methods based on the best-basis WP representation have shown significant coding gains for some image classes compared with methods using a fixed dyadic structured wavelet basis, at the expense however, of considerably higher computational complexity. A modification of the best-basis method, the so-called complexity constrained best-basis algorithm (CCBB), is proposed which parameterises the complexity gap between the fast (standard) wavelet transform and the best wavelet packet basis of a maximal WP library. This new approach allows a `suboptimal' best basis to be found with respect to a given budget of computational complexity or, in other words, it offers an instrument to control the trade-off between compression speed and, coding efficiency. Experimental results are presented for image coding applications showing a highly nonlinear relationship between the rate-distortion performance and the computational complexity in such a way that a relatively small increase in complexity with respect to the standard wavelet basis results in a relatively high rate distortion gain     

Wavelet-based very low bit-rate video coding using image warpingand overlapped block motion compensation

The authors present an algorithm for very low bit-rate video coding that combines new ideas in motion estimation, wavelet filter design, and wavelet-based coding techniques. A new motion compensation technique using image warping and overlapped block motion compensation is proposed to reduce temporal redundancies in a given image sequence. This combined motion model has the advantage of representing more complex motion than simple block matching schemes. To further improve the quality of the temporal prediction, an adaptive grid with variable density according to the varying motion activity of a given scene is generated. An adaptively switched high-quality texture interpolation is employed to cope with the problem of fractional displacements in such a way that both objective and subjective reconstruction quality is improved. Spatial decorrelation of the motion compensated residual images is performed using an one-parametric family of biorthogonal infinite impulse response (IIR) wavelet filters coupled with the highly efficient pre-coding scheme of `partitioning, aggregation and conditional coding' (PACC). Experimental results demonstrate significant improvements in objective quality of 1.0-2.3 dB PSNR in comparison to the H.263+ test model TMN10 using advanced coding options. In addition, the authors' intracoding method provides a performance gain of 0.5 dB PSNR on the average for a test suite of various still images when compared to the emerging still image coding standard JPEG-2000     

The H.264/MPEG4 advanced video coding standard and its applications

H.264/MPEG4-AVC is the latest video coding standard of the ITU-T video coding experts group (VCEG) and the ISO/IEC moving picture experts group (MPEG). H.264/MPEG4-AVC has recently become the most widely accepted video coding standard since the deployment of MPEG2 at the dawn of digital television, and it may soon overtake MPEG2 in common use. It covers all common video applications ranging from mobile services and videoconferencing to IPTV, HDTV, and HD video storage. This article discusses the technology behind the new H.264/MPEG4-AVC standard, focusing on the main distinct features of its core coding technology and its first set of extensions, known as the fidelity range extensions (FRExt). In addition, this article also discusses the current status of adoption and deployment of the new standard in various application areas.