A method of encoding video data in a merge mode, comprising: determining motion information of a current block; generating a prediction block of the current block using the motion information; generating a residual block using the current block and the prediction block; transforming the residual block to generate a transformed block; quantizing the transformed block using a quantization parameter to generate a quantized block; scanning coefficient components of the quantized block using a diagonal scan; entropy-coding the scanned coefficient components of the quantized block; and encoding the motion information, wherein encoding the motion information comprises the sub-steps of: deriving spatial merge candidates; deriving a temporal merge candidate; constructing a merge list using available spatial and temporal merge candidates; selecting a merge predictor among merge candidates of the merge list; and encoding a merge index specifying the merge predictor, wherein when the current block is a second prediction block partitioned by asymmetric partitioning from a current coding unit, the spatial merge candidate corresponding to a first prediction unit partitioned by the asymmetric partitioning is not to be listed on the merge list, wherein the quantization parameter is determined per a quantization unit and is encoded using a quantization parameter predictor, and wherein the quantization parameter is a quantization step size, wherein the quantization parameter predictor is generated by using quantization parameters of neighboring coding units and a quantization parameter of a previous coding unit such that if two or more quantization parameters are available among a left quantization parameter, an above quantization parameter and a previous quantization parameter of the current coding unit, the quantization parameter predictor is generated using an average of the first two available quantization parameters among the left quantization parameter, the above quantization parameter and the previous quantization parameter in that order, and if only one is available among the left quantization parameter, the above quantization parameter and the previous quantization parameter, the available quantization parameter is set as the quantization parameter predictor. determining motion information of a current block; generating a prediction block of the current block using the motion information; generating a residual block using the current block and the prediction block; transforming the residual block to generate a transformed block; quantizing the transformed block using a quantization parameter to generate a quantized block; scanning coefficient components of the quantized block using a diagonal scan; entropy-coding the scanned coefficient components of the quantized block; and encoding the motion information, wherein encoding the motion information comprises the sub-steps of: deriving spatial merge candidates; deriving a temporal merge candidate; constructing a merge list using available spatial and temporal merge candidates; selecting a merge predictor among merge candidates of the merge list; and encoding a merge index specifying the merge predictor, deriving spatial merge candidates; deriving a temporal merge candidate; constructing a merge list using available spatial and temporal merge candidates; selecting a merge predictor among merge candidates of the merge list; and encoding a merge index specifying the merge predictor, wherein when the current block is a second prediction block partitioned by asymmetric partitioning from a current coding unit, the spatial merge candidate corresponding to a first prediction unit partitioned by the asymmetric partitioning is not to be listed on the merge list, wherein the quantization parameter is determined per a quantization unit and is encoded using a quantization parameter predictor, and wherein the quantization parameter is a quantization step size, wherein the quantization parameter predictor is generated by using quantization parameters of neighboring coding units and a quantization parameter of a previous coding unit such that if two or more quantization parameters are available among a left quantization parameter, an above quantization parameter and a previous quantization parameter of the current coding unit, the quantization parameter predictor is generated using an average of the first two available quantization parameters among the left quantization parameter, the above quantization parameter and the previous quantization parameter in that order, and if only one is available among the left quantization parameter, the above quantization parameter and the previous quantization parameter, the available quantization parameter is set as the quantization parameter predictor.