As exposition, I think this piece falls into the trap of explaining the specifics of CABAC as if it was a concrete object like an internal combustion engine. Ar

As exposition, I think this piece falls into the trap of explaining the specifics of CABAC as if it was a concrete object like an internal combustion engine. Arithmetic coding is not difficult to visualize, as the well-known Dasher applet shows, and there's no problem with giving a very general and abstract explanation rather than working through a specific implementation. The question of the size of the alphabet is orthogonal to the topic of context adaptation, and I think CA could be clearly introduced in a generic setting before picking an alphabet size. Dasher uses the actual alphabet (well, a character set) which makes the predictive aspect of context adaptation obvious to anyone who has played with Markov chains. Actually the Wikipedia page for CABAC seems a bit confused and fanboyish on some points. Maybe I am missing something, but "It encodes binary symbols, which keeps the complexity low and allows probability modelling for more frequently used bits of any symbol" sounds like garbage to me...