H.264/AVC entropy decoder complexity analysis and its applications
Journal of Visual Communication and Image Representation
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The problem of H.264/AVC decoder complexity modeling and its applications to control the decoding complexity are studied in this research. The encoder integrated with the decoding complexity model and the associated decoding complexity control algorithm can generate decoder-friendly bit streams in the sense that compressed bit streams can be easily decoded on a particular decoding platform at a lower complexity and/or to meet various decoding complexity constraints.First, a decoding complexity model for H.264/AVC motion compensation process (MCP) and spatial compensation process (SCP) is proposed and applied to the H.264/AVC decoding complexity reduction. The proposed complexity model considers a rich set of inter and intra prediction modes of H.264/AVC as well as the relationship between motion vectors (MVs), frame sizes and the distribution of selected reference frames, which turn out to be highly related to cache management efficiency. An H.264/AVC encoder equipped with the complexity model can estimate the decoding complexity and then choose the best inter- or intra-prediction mode to meet the decoding complexity constraint of a target decoding platform. A decoding complexity control scheme for H.264/AVC MCP and SCP is also presented. The performance of the proposed complexity model and the complexity control scheme in video decoding complexity reduction is demonstrated experimentally. Second, two decoding complexity models for H.264/AVC entropy coding are proposed. It has been observed that entropy decoding demands a higher computational complexity for high rate video streams (e.g., high definition contents) due to a larger number of non-zero quantized transformed coefficients (QTCs) and MVs, which motivates our study on this topic. There are two entropy coding modes in H.264/AVC: the context-based adaptive binary arithmetic coding (CABAC) and the variable length coding (VLC). Furthermore, the latter mode consists of two tools: universal variable length coding (UVLC) and content-based adaptive variable length coding (CAVLC). In H.264/AVC, CABAC is used to encode all syntax elements while CAVLC and UVLC are used to encode QTCs and header data, respectively. The proposed entropy decoding complexity models consist of two parts. Its first part is designed for the source data (i.e. , QTCs) while its second part aims at effective coding of the header data. Both parts are verified experimentally. Complexity control for H.264/AVC entropy decoding is also examined.Finally, the decoding complexity model of the H.264 deblocking filter (DBF) is studied. The DBF process consists of three main modules: boundary strength computation, edge detection, and low-pass filtering. Complexities of all three of them are considered in our proposed model. DBF-based decoding complexity control is also investigated. It is shown experimentally that the proposed complexity model provides good complexity estimates. Besides, the H.264 encoder equipped with the decoding complexity model and complexity control algorithms can generate bit streams to save a significant amount of decoding complexity while offering quality similar to those generated by a typical H.264 encoder.