1. A method comprising: accessing, without initially decoding, arithmetically encoded data, the arithmetically encoded data comprising data encoded with an arithmetic code, and the encoded data including at least a first coded portion and a second coded portion, wherein the first and second coded portions have been coded with a code having memory, such that decoding the second coded portion relies on an output from decoding the first coded portion; and determining a modified first arithmetically coded portion such that the second coded portion is decodable to produce a common result based on either an output from decoding the first coded portion or an output from decoding the modified first arithmetically coded portion, wherein determining comprises determining a modified first arithmetically coded portion that generates a Context-based Adaptive Binary Arithmetic Coding (CABAC) state value that is the same as a CABAC state value generated by the first coded portion.
15. The method of claim 1 wherein: the encoded data comprises entropy encoded data, the first coded portion comprises a syntax element, and the modified first arithmetically coded portion comprises a modification of the syntax element.