Motion vector prediction method and apparatus for encoding or decoding video

An apparatus for encoding an image, the apparatus comprising:

• at least one processor configure to:
• generate a collocated index for determining a collocated picture from among pictures restored before a current picture;
• when one of a reference picture of a collocated block included in the collocated picture and a reference picture of a current block is determined as a long-term reference picture, and the other one of the reference picture of the collocated block and the reference picture of the current block is determined as a short-term reference picture, determine that a motion vector of the collocated block is un-available so that the motion vector of the collocated block is not used to predict a motion vector of the current block;
• when both of the reference picture of the collocated block and the reference picture of the current block are determined as long-term reference pictures, obtain a temporal motion vector prediction candidate without scaling the motion vector of the collocated block;
• generate information about a long-term reference picture for determining whether the reference picture of the current block is the long-term reference picture;
• determine a motion vector predictor of the current block from among motion vector prediction candidates, comprising the temporal motion vector prediction candidate;
• and
• generate prediction information of a candidate block as prediction information of the current block that indicates the candidate block used to derive the motion vector predictor of the current block,
• wherein the scaling is based on a ratio of a distance (Td) between the collocated picture and the reference picture of the collocated block and a distance (Tb) between the current picture and the reference picture of the current block.

A method for encoding an image, the method comprising:

• generating a collocated index for determining a collocated picture from among pictures restored before a current picture;
• when one of a reference picture of a collocated block included in the collocated picture and a reference picture of a current block is determined as a long-term reference picture, and the other one of the reference picture of the collocated block and the reference picture of the current block is determined as a short-term reference picture, determining that a motion vector of the collocated block is un-available so that the motion vector of the collocated block is not used to predict a motion vector of the current block;
• when both of the reference picture of the collocated block and the reference picture of the current block are determined as long-term reference pictures, obtaining a temporal motion vector prediction candidate without scaling the motion vector of the collocated block;
• generating information about a long-term reference picture for determining whether the reference picture of the current block is the long-term reference picture;
• determining a motion vector predictor of the current block from among motion vector prediction candidates, comprising the temporal motion vector prediction candidate;
• and
• generating prediction information of a candidate block as prediction information of the current block that indicates the candidate block used to derive the motion vector predictor of the current block,
• wherein the scaling is based on a ratio of a distance (Td) between the collocated picture and the reference picture of the collocated block and a distance (Tb) between the current picture and the reference picture of the current block.

A non-transitory computer-readable storage medium storing a bitstream generated by at least one processor, the bitstream comprising:

• a collocated index for determining a collocated picture from among pictures restored before a current picture;
• information about a long-term reference picture for determining whether a reference picture of a current block is a long-term reference picture;
• and
• prediction information of a candidate block as prediction information of the current block that indicates the candidate block used to derive a motion vector predictor of the current block,
• wherein when one of a reference picture of a collocated block included in the collocated picture and the reference picture of a current block is determined as the long-term reference picture, and the other one of the reference picture of the collocated block and the reference picture of the current block is determined as a short-term reference picture, a motion vector of the collocated block is determined as un-available so that the motion vector of the collocated block is not used to predict the motion vector of the current block;
• when both of the reference picture of the collocated block and the reference picture of the current block are determined as long-term reference pictures, a temporal motion vector prediction candidate is obtained without scaling the motion vector of the collocated block;
• wherein the motion vector predictor of the current block is determined from among motion vector prediction candidates, comprising the temporal motion vector prediction candidate
• wherein the scaling is based on a ratio of a distance (Td) between the collocated picture and the reference picture of the collocated block and a distance (Tb) between the current picture and the reference picture of the current block.