Thomas Wiegand

Scalable video coding (SVC) is an extension of H.264/AVC, which is currently being developed by the Joint Video Team. SVC supports any combination of temporal, spatial, and SNR scalability, but there is no special treatment for the case that two or more different bit-depths have to be supported by the scalable bit-stream. There is a number of applications (especially in the HD area) which would benefit from a design where an H.264/AVC conforming base layer with a sample bit-depth of typically 8 bit is extended in a backwards compatible way by an higher bit-depth enhancement layer. In this paper we present new techniques which can be used to achieve bit-depth scalability and show experimental results.

A streaming system based on the scalable video coding (SVC) extension of H.264/AVC is shown. SVC allows for data rate adaptation without re-encoding just by dropping packets of the bit stream. By that, it enables for instance multicast services to clients of heterogeneous capabilities at the same time, while consuming less bit rate compared to simulcasting the services. Additionally, the robustness of a streaming connection against packet losses can be significantly increased if the different layers of the coded video stream are unequally protected by a forward error correction scheme. In this case, users will experience graceful degradation of image quality rather than visible errors or interruptions. The introduction of new services using SVC can also take advantage of a backward-compatible base layer. Different use cases for SVC streaming in wireless IP networks and selected simulation results of the improved error robustness for a DVB-H wireless transmission are presented.

Fidelity scalability involves the refinement of residual texture information. The entropy coding of texture refinement information in the scalable video coding (SVC) extension of H.264/AVC relies on a simple statistical model that is tuned to an encoder-specific way of quantization for generating a single fidelity enhancement layer on top of the backward compatible base layer. For fidelity enhancement layers above the first layer, we demonstrate how and why the current model fails to properly reflect the statistics of texture refinement information. By analyzing the specific properties of the typical quantization process in fidelity scalable coding of SVC, we are able to derive a generic modeling approach for coding of refinement symbols, independent of the specific choice of dead-zone parameters and classification rules. Experimental results for a broad range of quantization parameters show averaged bit-rate savings of around 5% (relative to the total bit rate) by using our proposed context modeling approach for a representative set of video sequences in a test scenario including up to three fidelity enhancement layers.

Coding of video sequences using hierarchical B pictures in the joint scalable video model (JSVM) for the scalability amendment of H.264/AVC has the benefit of improved rate distortion efficiency relative to other known temporal decomposition structures, besides providing temporal scalability. In the operational encoder control of the JSVM, the inter-picture dependencies within a hierarchical B picture structure are considered using a heuristic, where pictures that are more frequently used for motion compensation are coded with higher fidelity compared to pictures that are less often used for motion compensation. In this paper, we describe an approach where the dependencies introduced by motion compensation are also considered when selecting transform coefficient values. Our experimental results using an H.264/AVC conforming encoder show bit rate reductions of up to 10% compared to the quantization method used by JSVM.

The scalable video coding (SVC) extension of H.264/AVC was recently standardized. The encoder control that is described in the joint scalable video model for SVC specifies a bottom-up process in which first the base layer and then the enhancement layer is encoded. The base layer is encoded conforming to H.264/AVC without considering its impact on enhancement layers, which limits the achievable enhancement layer coding efficiency. The losses relative to single-layer H.264/AVC coding are unevenly distributed between base and enhancement layers. In this paper, we present a multi-layer encoder control for SVC, by which we can trade off coding efficiency for base and enhancement layers and generally improve the efficiency of spatial and fidelity scalable coding.

In this paper, an investigation of H.264/MPEG4-AVC conforming coding with hierarchical B pictures is presented. We analyze the coding delay and memory requirements, describe details of an improved encoder control, and compare the coding efficiency for different coding delays. Additionally, the coding efficiency of hierarchical B picture coding is compared to that of MCTF-based coding by using identical coding structures and a similar degree of encoder optimization. Our simulation results turned out that in comparison to the widely used IBBP...structure coding gains of more than 1 dB can be achieved at the expense of an increased coding delay. Further experiments have shown that the coding efficiency gains obtained by using the additional update steps in MCTF coding are generally smaller than the losses resulting from the required open-loop encoder control