Parallel Scalability of H.264

An important question is whether emerging and future applications exhibit sufficient parallelism, in particular thread-level parallelism (TLP), to exploit the large numbers of cores future CMPs are expected to contain. As a case study we investigate the parallel scalability of the H.264 decoding process. Previously proposed parallelization strategies such as slice-level, frame-level, and intra-frame macroblock (MB) level parallelism, are not sufficiently scalable. We therefore propose a novel strategy, called 3D-Wave, which is mainly based on the observation that inter-frame dependencies have a limited spatial range. Because of this, certain MBs of consecutive frames can be decoded in parallel. The 3D-Wave strategy allows 4000 to 9000 MBs to be processed in parallel, depending on the input sequence. We also perform a case study to assess the practical value and possibilities of the 3D-Wave strategy. The results show that our strategy provides sufficient parallelism to efficiently exploit the capabilities of future manycore CMPs.