A method of decoding a video includes determining an initial value of a quantization parameter (QP) used to perform inverse quantization on coding units included in a slice segment, based on syntax obtained from a bitstream; determining a slice-level initial QP for predicting the QP used to perform inverse quantization on the coding units included in the slice segment, based on the initial value of the QP; and determining a predicted QP of a first quantization group of a parallel-decodable data unit included in the slice segment, based on the slice-level initial QP.