Prediction-based macroblock mode mapping for video coding

This paper describes an efficient entropy coding method for macroblock modes in H.264 based on the statistical information of the previous frame. H.264/MPEG-4 AVC video coding introduces some new macroblock sub-types (modes) that allow for better rate-distortion (R-D) coding. These modes are coded with a fixed mapping table when context adaptive variable length coding (CAVLC) is used. Based on our experiments on the sequences recommended by the Video Coding Experts Group (VCEG) common test conditions, the average number of bits to code those modes is 15% of that of the total bits for coding P-frames. The proposed method maps the more frequently used modes to shorter codeword instead of using a fixed mapping table, and reduces about 10-20% of the bits used for coding the inter modes. This method can be applied to other syntax elements, e.g. coded block pattern (CBP), as well.