Abstract: When a digital video signal is compressed, the amount of resulting data is predicted and the quantization level is controlled so as to obtain a constant bit rate. The prediction is made by computing a linear combination of a standard deviation and a number of non-zero coefficients, or by computing a sum of absolute differences between adjacent pixel values, or by computing a dynamic range of pixel values. The bit rate can also be controlled by deleting high-frequency coefficients. To avoid image degradation, the quantization level can also be controlled according to the sensitivity of small image areas to quantization noise. Sensitivity is determined by dividing an area into subblocks, which may overlap, and calculating statistics in each subblock. To reduce the amount of computation required in motion estimation, chrominance motion vectors are derived from luminance motion vectors.