1. A video codec apparatus, comprising: an inverse scanning unit configured to generate a quantized block by inversely scanning quantized coefficient information in the unit of subset when a size of a transform unit is larger than 4×4; an inverse quantization unit configured to generate a quantization step size predictor, restore a quantization step size by adding the quantization step size predictor and a remaining quantization step size, and generate a transform block by inversely quantizing the quantized block using the quantization step size; an inverse transform unit configured to restore a residual block by inversely transforming the transform block; and an inter prediction unit configured to determine a motion vector predictor of a current prediction unit, restore a motion vector of the current prediction unit using the motion vector predictor, and generate a prediction block of the current prediction unit using the motion vector, wherein the motion vector predictor is an available spatial motion vector candidate or an available temporal motion vector candidate and the temporal motion vector candidate is an available motion vector encountered first when retrieving motion vectors in the order of motion vector of a first predetermined position and motion vector of a second predetermined position in a reference picture, the quantization step size predictor is determined using quantization step size of: 1) a left coding unit neighboring a current coding unit, 2) an above coding unit neighboring the current coding unit, and 3) a previous coding unit in scan order within a same frame or slice as the current coding unit, and when the quantization step sizes of the left coding unit and the above coding unit are unavailable, the inverse quantization unit determines the quantization step size of the previous coding unit as the quantization step size predictor of the current coding unit.