Video encoding method and video decoding method

1. A video decoding method comprising the steps of:

selecting a prediction mode to be performed among a plurality of prediction modes including an intra-prediction mode and an inter-prediction mode;

calculating a predictive motion vector, in case that the inter-prediction mode is selected as the prediction mode to be performed;

calculating a motion vector by summing the predictive motion vector calculated in the predictive motion vector calculating step and a differential motion vector decoded from a coded stream, in case that the inter-prediction mode is selected as the prediction mode to be performed; and

performing an inter-prediction process of the selected prediction mode using the motion vector calculated in the motion vector calculating step, in case that the inter-prediction mode is selected as the prediction mode to be performed,

wherein the predictive motion vector calculating step includes:

a first process to select a plurality of candidate blocks among blocks decoded prior to a block to be decoded, the candidate blocks are selected from five or more blocks, the five or more blocks including peripheral blocks in the same frame as the block to be decoded and blocks in a different frame from the block to be decoded,

a second process to use any one of a first value and a second value when a difference between the first value and the second value in motion vector values of the plurality of candidate blocks is within a predetermined threshold,

a third process to make a motion vector list listing a plurality of motion vector values including the motion vector value of the first value or the second value selected in the second process and a motion vector value other than the first value and the second value in the motion vector values of the plurality of candidate blocks selected in the first process,

a fourth process to retrieve selection information from the coded stream, and

a fifth process to select one motion vector value among the plurality of motion vector values listed in the motion vector list,

wherein the one motion vector value selected from the plurality of motion vector values listed in the motion vector list is determined based on the selection information regardless of the differential motion vector,

wherein the number of the plurality of motion vector values listed in the motion vector list is smaller than five,

wherein the peripheral blocks in the same frame as the block to be decoded, referred to in the first process, includes a peripheral block, located at an upper-left side of the block to be decoded, and

wherein the predictive motion vector from the block to be decoded to a block in a reference frame which is located at an earlier time position than the frame of the block to be decoded, is calculated in the predictive motion vector calculating step.

2. A method comprising:

selecting a prediction mode to be performed among a plurality of prediction modes including an intra-prediction mode and an inter-prediction mode;

calculating a predictive motion vector in case the inter-prediction mode is selected as the prediction mode to be performed;

calculating a motion vector by summing the calculated predictive motion vector and a differential motion vector decoded from a coded stream, in case the inter-prediction mode is selected as the prediction mode to be performed; and

performing an inter-prediction process of the selected prediction mode using the calculated motion vector in case the inter-prediction mode is selected as the prediction mode to be performed,

wherein the calculating the predictive motion vector includes:

selecting a plurality of candidate blocks among blocks decoded prior to a block to be decoded, the candidate blocks being selected from five or more blocks, the five or more blocks including peripheral blocks in the same frame as the block to be decoded and blocks in a different frame from the block to be decoded,

using one of a first value or a second value when a difference between the first value and the second value in motion vector values of the plurality of candidate blocks is within a predetermined threshold,

generating a motion vector list listing a plurality of motion vector values including the motion vector value of the first value or the second value, and a motion vector value other than the first value and the second value in the motion vector values of the plurality of candidate blocks,

retrieving selection information from the coded stream, and

selecting one motion vector value among the plurality of motion vector values listed in the motion vector list,

wherein the one motion vector value selected from the plurality of motion vector values listed in the motion vector list is determined based on the selection information regardless of the differential motion vector,

wherein the number of the plurality of motion vector values listed in the motion vector list is smaller than five,

wherein the peripheral blocks in the same frame as the block to be decoded, referred to in the selecting the plurality of candidate blocks, includes a peripheral block located at an upper-left side of the block to be decoded, and

wherein the predictive motion vector from the block to be decoded to a block in a reference frame which is located at an earlier time position than the frame of the block to be decoded, is calculated in the calculating the predictive motion vector.