Use of extended samples during search in decoder-side motion refinement

A non-transitory computer-readable media storing computer instructions for inter prediction of a block of a picture, wherein the computer instructions are executed by one or more processors, to cause the one or more processors to perform the operations including:

• determining a first prediction block based on an initial first motion vector of a current block in a first reference picture of the current block;
• obtaining a first extension block based on the first prediction block, wherein the first extension block comprises the first prediction block and at least one boundary block adjacent to the first prediction block;
• obtaining one or more first reference blocks in the first reference picture, wherein each first reference block is associated with a combination of the initial first motion vector and one of one or more motion vector offsets, and wherein a size of the first reference block is the same as a size of the first extension block;
• obtaining a target motion vector offset with a smallest cost among the one or more motion vector offsets based on a matching cost comparison involving the one or more first reference block and an initial prediction block, and wherein the initial prediction block is obtained from the first extension block;
• determining a refined first motion vector of the current block, wherein the refined first motion vector is a combination of the initial first motion vector and the target motion vector offset;
• and
• obtaining a refined prediction block of the current block based on the refined first motion vector.

An inter prediction method, applied to an apparatus comprising a video coder and a video data memory, the method comprising:

• determining a first prediction block based on an initial first motion vector of a current block in a first reference picture of the current block;
• obtaining a first extension block based on the first prediction block, wherein the first extension block comprises the first prediction block and at least one boundary block adjacent to the first prediction block;
• obtaining one or more first reference blocks in the first reference picture, wherein each first reference block is associated with a combination of the initial first motion vector and one of one or more motion vector offsets, and wherein a size of the first reference block is the same as a size of the first extension block;
• obtaining a target motion vector offset with a smallest cost among the one or more motion vector offsets based on a matching cost comparison involving the one or more first reference block and an initial prediction block, and wherein the initial prediction block is obtained from the first extension block;
• determining a refined first motion vector of the current block, wherein the refined first motion vector is a combination of the initial first motion vector and the target motion vector offset;
• and
• obtaining a refined prediction block of the current block based on the refined first motion vector.