Study And Optimization Of H.264 Video Coding Standard

H.264 is a new video coding standard jointly developed by ITU-T and ISO MPEG. It has drawn a lot of attention because of its excellent coding performance. However, the high computational complexity of H.264 holds it back from practical uses. In this paper, we'll focus on optimizations of H.264 encoder at algorithm level and instruction level. Motion estimation is the most important module in a video encoder. The algorithm can directly impact the speed and performance of the encoder. H.264 introduces 7 block size modes, and improves the motion compensation accuracy to 1/4-pixle. Previous studies on motion estimation mainly focus on integer-pixel motion estimation, and very few deal with fast mode decision. In this paper, we'll analyze the correlation between the best modes of different accurate levels(integer-pixel,1/2-pixel,and 1/4-pixel), and based on this, we propose a new fast mode decision algorithm. This algorithm can simplify the procedure of mode decision and significantly reduce the computational complexity of sub-pixel motion estimation. The loss of coding performance is negligible.After optimizing H.264 encoder at algorithm level, we'll further optimize the computationally intensive modules in H.264 encoder using Intel's SSE-2 instruction set and significantly speed up the encoder.Finally, based on works in previous chapters, we develop a multi-thread H.264 Codec static library. The Codec uses context-switching technique and supports simultaneous encoding of multiple channels. In a PC with Intel Pentium 4 CPU and 256M SDRAM, the single-channel encoding speed is above 40f/s for QCIF sequences and 10f/s for CIF sequences.