1. A computer-implemented method of video encoding comprising: computing spatial variance for video data in a block of a video sequence; estimating a first bit-rate based on the spatial variance, a transform coefficient threshold, and variance multiplicative factors empirically determined for first transform coefficients; and encoding the block based on the first bit-rate; wherein estimating a first bit-rate comprises estimating the first bit-rate as a value given by φ × ∑ i ⁢ exp ( - 2 ⁢ T i σ spatial ) wherein φ is a number of bits for encoding the first transform coefficients, Ti is a ratio of the transform coefficient threshold and a variance multiplicative factor of the variance multiplicative factors for the ith first transform coefficient, and σ is the spatial variance.