Dynamic Table Lookup for the Entropy Coding of P-frames in H.264

In the H.264 standards, the default block size is reduced to 4x4. As a result, it becomes quite possible that a quantized residue block in the current P-frame is matched (either identical or very similar) to one of the previously-coded blocks. Thus, the encoding of any current block that contains a few non-zero coefficients could be made more efficient if we transmit the relevant information of the matched block instead of coding it with standard variable-length coding. To this end, all previously-coded blocks should be carefully maintained so as to construct a codebook. In this paper, we study how such codebook is formed initially, how to use this newly formed codebook to encode some blocks in the current frame, and how this codebook is updated dynamically during the encoding process. We also propose various modifications on the H.264 encoding table in order to maintain the synchronization between the modified encoder and decoder after the lookup-table is added to the system. Testing is performed based on different codebook setup. Experiment results show that the bit-count per frame can be saved by about 6-9% after applying the proposed codebook technique with very little degradation on the video quality.