Encoding method and device thereof, and decoding method and device thereof

1. A video decoding method comprising:

obtaining, from a bitstream, first inter prediction mode permission information indicating whether a first inter prediction mode for predicting a motion vector is allowed for an upper data unit;

when the first inter prediction mode is allowed for the upper data unit based on the first inter prediction mode permission information, obtaining, from the bitstream, correction distance range information;

when the first inter prediction mode is allowed for the upper data unit, determining whether the first inter prediction mode is applied to a current block included in the upper data unit;

when the first inter prediction mode is applied to the current block, obtaining information about a motion vector from the bitstream and determining a base motion vector indicated by the information about the motion vector from a motion vector candidate list of the current block;

obtaining, from the bitstream, information about a correction distance and information about a correction direction;

determining a correction distance by using the information about the correction distance and a correction distance range indicated by the correction distance range information;

determining a correction direction by using the information about the correction direction;

determining a motion vector of the current block by correcting the base motion vector according to the correction distance and the correction direction; and

reconstructing the current block based on the motion vector of the current block,

wherein the correction distance range information indicates one of a plurality of correction distance candidate sets,

wherein one correction distance set from among the plurality of correction distance candidate sets comprises a preset number of correction distance candidates, and

wherein a correction distance set is selected, from among the plurality of correction distance candidate sets, according to the correction distance range information, the correction distance is indicated by the information about the correction distance, among the preset number of correction distance candidates included in the selected correction distance set, and the base motion vector is corrected by using the correction distance.

2. The video decoding method of claim 1 , wherein the upper data unit is one of a sequence, a picture, and a slice.

3. The video decoding method of claim 1 , further comprising:

when the first inter prediction mode is not applied to the current block, applying a merge mode other than the first inter prediction mode to the current block; and

by using a motion vector index obtained from the bitstream, determining a motion vector candidate indicated by the motion vector index from a merge motion vector candidate list, and determining the motion vector of the current block by using the motion vector candidate without the correction distance and the correction direction.

4. A video encoding method comprising:

generating first inter prediction mode permission information indicating whether a first inter prediction mode for predicting a motion vector is allowed for an upper data unit;

when the first inter prediction mode is allowed for the upper data unit, generating correction distance range information;

determining a motion vector of a current block;

when the first inter prediction mode is allowed for the upper data unit, determining whether the first inter prediction mode is applied to the current block;

when the first inter prediction mode is applied to the current block, determining a base motion vector from a motion vector candidate list of the current block and generating information about a motion vector for indicating the base motion vector from the motion vector candidate list;

determining a correction distance and a correction direction for correction of the base motion vector based on a difference between the motion vector and the base motion vector;

generating information about a correction distance for indicating the correction distance selected in a correction distance range;

generating information about a correction direction for indicating the correction direction; and

outputting a bitstream comprising the first inter prediction mode permission information, the correction distance range information, the information about the motion vector, the information about the correction distance, and the information about the correction direction,

wherein one correction distance set from among a plurality of correction distance candidate sets comprises a preset number of correction distance candidates, and

wherein the correction distance range information indicates a correction distance set selected from among the plurality of correction distance candidate sets, the information about the correction distance indicates the correction distance selected from among the preset number of correction distance candidates included in the selected correction distance set, and the correction distance is to be used to correct the base motion vector.

5. A video encoding apparatus comprising a processor configured to:

generate first inter prediction mode permission information indicating whether a first inter prediction mode for predicting a motion vector is allowed for an upper data unit;

when the first inter prediction mode is allowed for the upper data unit, generate correction distance range information;

determine a motion vector of a current block;

when the first inter prediction mode is allowed for the upper data unit, determine whether the first inter prediction mode is applied to the current block;

when the first inter prediction mode is applied to the current block, determine a base motion vector from a motion vector candidate list of the current block and generate information about a motion vector for indicating the base motion vector from the motion vector candidate list;

determine a correction distance and a correction direction for correction of the base motion vector based on a difference between the motion vector and the base motion vector;

generate information about a correction distance for indicating the correction distance selected in a correction distance range;

generate information about a correction direction for indicating the correction direction; and

output a bitstream comprising the first inter prediction mode permission information, the correction distance range information, the information about the motion vector, the information about the correction distance, and the information about the correction direction,

wherein one correction distance set from among a plurality of correction distance candidate sets comprises a preset number of correction distance candidates, and

wherein the correction distance range information indicates a correction distance set selected from among the plurality of correction distance candidate sets, the information about the correction distance indicates the correction distance selected from among the preset number of correction distance candidates included in the selected correction distance set, and the correction distance is to be used to correct the base motion vector.