1. A method of decoding video data using a merge mode, the method comprising: constructing a merge list using available spatial and temporal merge candidates; determining a merge candidate on the merge list corresponding to a merge index as motion information of a current prediction unit; generating a predicted block of the current prediction unit using the motion information; generating a transformed block by inverse-quantizing a block of quantized coefficients using a quantization parameter; generating a residual block by inverse-transforming the transformed block; and generating a reconstructed block using the predicted block and the residual block, wherein the merge list contains a predetermined number of merge candidates among the available spatial and temporal merge candidates, wherein the quantization parameter is derived per a quantization unit, wherein a minimum size of the quantization unit is adjusted per picture, wherein the quantization parameter is derived using a differential quantization parameter and a quantization parameter predictor, wherein if two or more quantization parameters are available among a left quantization parameter, an above quantization parameter and a previous quantization parameter of a current coding unit, the quantization parameter predictor is generated using two available quantization parameters determined according to a predetermined order among the left quantization parameter, the above quantization parameter and the previous quantization parameter, wherein if a left and an above quantization parameter of a current coding unit are not available, a previous quantization parameter is set as the quantization parameter predictor, wherein the differential quantization parameter is restored using a bin string indicating an absolute value of the differential quantization parameter and a bin indicating a sign of the differential quantization parameter, and wherein the bin string and the bin are derived from a picture parameter set.