1. Method for assessing the quality of a distorted version of a frame sequence, said method comprises the steps of, a) determining a last spatial distortion by comparing a block of a last frame of the sequence with a corresponding block of the distorted version of the last frame, b) determining, in a last-but-one frame, a best-matching block matching said block of the last frame best, c) determining a last-but-one spatial distortion by comparing the determined best-matching block of the last-but-one frame with a corresponding block of the distorted version of the last-but-one frame d) determining a spatio-temporal perceptual distortion value associated with said block using said determined distortions and using the determined spatio-temporal perceptual distortion value for assessing the quality.