Syntax – Based Arithmetic Coding Mode
In this mode the variable length codes are replaced with an arithmetic coder. The word length for the upper and lower limits is 16. The option specifies several different Cum Count tables that can be used for arithmetic coding. There are separate Cum Count tables for encoding motion vectors, intra DC component, and intra and inter coefficients.
Advanced Prediction Mode
In the baseline mode a single motion vector is sent for each macroblock. Recall that a macroblock consists of four 8 × 8 luminance blocks and two chrominance blocks. In the advanced prediction mode the encoder can send four motion vectors, one for each luminance block. The chrominance motion vectors are obtained by adding the four luminance motion vectors and dividing by 8. The resulting values are adjusted to the nearest half pixel position. This mode also allows for Overlapped Block Motion Compensation (OBMC). In this mode the motion vector is obtained by taking a weighted sum of the motion vector of the current block and two of the four vertical and horizontal neighboring blocks.