The present invention relates to a method and an apparatus for decoding a video stream, in which a computation of an inverse transformation is decreased in decoding the video stream. The decoding method according one embodiment comprises the steps of: receiving an encoded bit stream; extracting transformation coefficients from the bit stream; determining a max position of a block including at least one transformation coefficient being not 0 among the transformation coefficients; generating a control signal so the transformation coefficients corresponding the block are inversely transformed using the max position; and restoring video data by inversely transforming the transformation coefficients corresponding to the block on the basis of the control signal.
