Video coding efficiency is improved by jointly coding the x and y components
of motion vectors with a single variable length code. The motion vector components
for a block of pixels are predicted based on motion vectors of neighboring blocks
of pixels. The predicted x and y components are then jointly coded by assigning
a single variable length code corresponding to the pair of components, rather than
a separate code for each component. If the x and y components do not have a corresponding
entry in the coding table, they are coded with an escape code followed by fixed
length codes.