A method of encoding video data by an electronic device is provided. A block unit is determined from an image frame according to the video data. A line index is encoded in a bitstream based on a selected reference line of the block unit and is compared with a first predefined value to determine whether to encode a mode flag in the bitstream. A mode index is directly encoded in the bitstream for indicating a prediction mode of the block unit from a most probable mode (MPM) list of the block unit when the mode flag is not encoded. The mode flag is compared to a second predefined value for encoding the mode index when the mode flag is encoded in the bitstream to indicate whether the prediction mode is selected from the MPM list. The block unit is predicted based on the selected reference line and the prediction mode.