Research On HEVC Parallel Coding Method Based On COStream

In the era of Internet,multimedia data has increased explosively.Video data,as one of the most important multimedia data,has the characteristics of large amount of data and diversity of carrier.In order to reduce the storage cost and transmission cost,we need to compress the video data,many kinds of video encoding standards have been proposed.COStream programming language is based on dataflow programming model,which takes the data as the driving force,divides the communication and computation and realize parallel computing.Using COStream implement video coding to enhance the coding efficiency has good theoretical and practical significance.HEVC(High Efficiency video coding)/H.265 is the latest video encoding standard,it contains many parallel characteristics of different levels of data and tasks,including group of picture(GOP)parallel encoding,wavefront parallel encoding and entropy parallel encoding.The GOP is a set of pictures,there is no data dependency between GOPs,which can be optimized by using dataflow to parallelize them.The picture can be divided into many coding tree units(CTU),a picture contains multiple lines of CTU,that multiple CTU line can be parallel processing but needs to satisfy data dependencies,and dataflow can be used to parallelize them.HEVC uses context based adaptive binary arithmetic encoding(CABAC)for entropy encoding,it constructs the context probability model for syntax elements,after the context model is initialized,the syntax elements are entropy coded,syntax elements are sequentially encoded,the sequential processing of syntax elements forms a pipeline,the dataflow programming model can be used to parallelize them.In addition,entropy coding module is frequently called,the current mixed programming of COStream backend will create threads for each call,then destroy after execution,such implementation is not efficient enough,we use thread pool instead of threads creation and destruction to reduce runtime overhead.According to the above three modules of the dataflow characteristics,using COStream to parallelize them,other modules still using C++ to implementation,using COStream compiler to generate efficient executable program.The experiment use X86-64 multi-core server as the test platform,and the test speed of the program by using different video sequences.The experimental results show the practicability and effectiveness of the COStream programming language.