| JCTVC-B036 [D. He, G. Korodi, G. Martin-Cocher (RIM)] Improved parallelism for V2V entropy coding in HEVC
The V2V coding method described in the Test Model under Consideration for HEVC provides potentially significant throughput improvement over CABAC in ITU-T Rec. H.264 | ISO/IEC 14496-10. It is however observed that the context modeling process might become the bottleneck limiting the throughput of the whole decoding process. In order to improve throughput of coding residual data, a coding order that groups significant_coeff_flags and last_significant_coeff_flags according to their contexts is described. For these syntax elements, this coding order allows multiple bins to be processed in a single table lookup, whereas such table lookups are impractical with the existing coding order defined in ITU-T Rec. H.264 | ISO/IEC 14496-10.
Some coding efficiency impact – typically 0.5% or less.
A problem is that context modeling becomes the bottleneck (as it works serially).
Approach 1: For transform blocks: Use table lookup to determine the states for multiple bins simultaneously. In case of 4x4 blocks, this leads to minor increase in bit rate (larger blocks are somewhat more penalized, due to the fact that the number of possible states increases and needs to be limited in the table)
Approach 2: Idea to change the frequency in updating the states in context modelling (e.g. when update is performed at each 4th bin, 4 bins can be processed in parallel). This leads to a performance drop of 0.5 and 0.7 % for RaceHorses and BQMall, respectively. In fact, the assumption of 4x throughput in this case seems to be an upper limit.
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