Error-resilience improvement for block-transform video coders

An algorithm is presented to enhance the resilience of block-based video-coding algorithms against channel errors. The error-resilience algorithm described suggests the use of fixed length coding to alleviate the effect of Huffman coding on the synchronisation of the decode under erroneous conditions. The proposed mechanism modifies the order of transmission of the fixed-length video parameters to increase the chance of their arrival. Synchronisation words are sent at fixed-length intervals within the bit stream to reduce the possibility of the decoder falling on similar bit patterns within the bit stream. To limit the effect of error accumulation, the motion prediction process is halted and the differential coding of motion vectors is not applied. FEC techniques are applied on some error-sensitive segments of the reordered video bitstream. The effectiveness of the proposed error-resilience algorithm is evidenced by both subjective and objective results     

Method for error recovery of line spectral frequencies

The authors have exploited the ideas used in vector quantisation for error recovery of scalar quantised LSFs. The good performance of this method has provided high resistance of the LSFs to channel errors, outperforming other schemes by, possibly, a considerable margin. Better objective and subjective performances were obtained with this new method which obviates the need for more powerful FEC schemes for transmission over noisy channels.<>     

Analysis of Root Displacement Interpolation Method for Tunable Allpass Fractional-Delay Filters

One of the simplest ways of designing allpass fractional-delay filters with maximally flat group delays is by using the Thiran approximation by which the filter coefficients are calculated using a closed-form equation. However, due to the number of multiplications and divisions involved, the calculation of these coefficients is a computationally costly task and is not suitable for real-time applications. The analysis of a root-displacement-based interpolation method used in allpass tunable fractional delays is presented in this paper. The method allows continuous adjustments of the approximated fractional delay without the explicit calculation of a new set of filter coefficients. The transient error observed at the output due to the change of filter coefficients is analyzed. The direct and cascade implementations are compared with respect to their transient errors. An example application of the proposed method from the field of model-based sound synthesis is given.     

Adaptive streaming of multi-view video over P2P networks

In this paper, we propose a novel solution for the adaptive streaming of 3D representations in the form of multi-view video by utilizing P2P overlay networks to assist the media delivery and minimize the bandwidth requirement at the server side. Adaptation to diverse network conditions is performed regarding the features of human perception to maximize the perceived 3D. We have performed subjective tests to characterize these features and determined the best adaptation method to achieve the highest possible perceived quality. Moreover, we provide a novel method for mapping from scalable video elementary stream to torrent-like data chunks for adaptive video streaming and provide an optimized windowing mechanism that ensures timely delivery of the content over yanl?? gibi. The paper also describes techniques generating scalable video chunks and methods for determining system parameters such as chunk size and window length.     

Effects of finite-precision conversion on linear predictivecoefficients

Two novel methods are presented for improving the finite-precision conversion of linear prediction coefficients in the form of reflection coefficients. The first method is based on the improvement of the dynamic range of the intermediate variables in the Schur (1986) recursion using the block exponential format. For the second method, improvement is achieved by changing the statistical properties of the quantisation noise incurred during conversion. This is achieved with the addition of low-power uniform uncorrelated noise during the conversion from a lattice filter structure to direct-form filter structure. Statistical tests performed over a 1000 test frames reveal a significant reduction in both the variance and mean of the error compared with the standard fixed-point LPC filter     

Very low-bit-rate segmentation-based video coding using contour andtexture prediction

The most efficient video coding standard for low bit rates (around 64 kb/s) is the H.261 algorithm recommended by ITU-TS. However, in certain applications such as mobile audiovisual communications and videophone through PSTN, the available transmission bandwidth is very limited. Therefore codecs working at very low bit rates are required. The paper presents a segmentation-based video coding algorithm that can work at rates as low as 10 kb/s. A novel representation of the contour information using a number of control points is proposed to estimate the contour shapes and locations from the previous frame by using the motion information. The texture parameters are also predicted and only the residual values are entropy coded. In addition two novel postprocessing techniques for edge-profile smoothing and jagged-edge rectification are described     

Entropy coding of ITU G.728 speech parameters for low bit rateaudiovisual communications

Entropy coding principles are applied to the 16 kbit/s ITU G.728 speech codec. It is shown that the average bit rate can be reduced to 14.5 kbit/s without a significant increase in the codec complexity. In very low bit rate audiovisual communication applications such as the videophone, the saved bits can be used to improve the output video quality     

Motion adaptive intra refresh for MPEG-4

The sensitivity to error of a video bitstream often changes as the amount of motion within a scene changes. Taking this into account, a scheme that attempts to optimise error robustness by varying the amount of adaptive intra refresh blocks is presented. Simulation results demonstrate the benefits of the proposed technique     

Edge adaptive upsampling of depth map videos for enhanced free-viewpoint video quality

Quality enhancement of free-viewpoint videos is addressed for 3D video systems that use the colour texture video plus depth map representation format. More specifically, a novel and efficient shape adaptive filter is presented for upsampling depth map videos that are of lower resolution than their colour texture counterparts. Either measurement or estimation of depth map videos can take place at lower resolution. At the same time, depth map reconstruction takes place at low resolution if reduced resolution compression techniques are utilised. The proposed design is based on the observation that significant transitions in depth intensity across depth map frames influence the overall quality of generated free-viewpoint videos. Hence, sharpness and accuracy in the free-viewpoint videos rendered using 3D geometry via depth maps, especially across object borders, are targeted. Accordingly, significant enhancement of rendered free-viewpoint video quality is obtained when the proposed method is applied on top of MPEG spatial scalability filters.