In one example, an apparatus for encoding video data includes a video encoder configured to scan a two-dimensional block of transform coefficients to produce a one-dimensional vector of the transform coefficients, determine values indicative of whether the transform coefficients in the one-dimensional vector are significant; and entropy encode at least one of the values using a context model selected based on at least a percentage of significant coefficients in a predetermined number of the values encoded before the at least one of the values.