Hardware friendly constrained motion vector refinement

An electronic apparatus comprising:

• circuitry configured to:
• determine whether to partition the current block of pixels for motion vector refinement based on whether the current block of pixels meet a particular condition;
• when the current block of pixels is partitioned for motion vector refinement, the circuitry is further configured to:
• partition the current block of pixels into a plurality of partitioned units;
• and
• for every partitioned unit among the plurality of partitioned units:
• identify a first motion vector and a second motion vector;
• refine the first and second motion vectors;
• compute distortion costs of the refined first motion vector and the refined second motion vector based on a difference between a first reference pixel set in a first reference frame indicated by the refined first motion vector and a second reference pixel set in a second reference frame indicated by the refined second motion vector, respectively, wherein the pixel sets are sub-sampling pixel data of a subset of the pixel data in only odd or even numbered lines of the pixel data according to the first and second motion vectors,
• wherein, when a plurality of distortion costs are calculated for the partitioned unit, the circuitry is further configured to derive a minimized distortion cost based on the plurality of distortion costs, and obtain a corresponding refined first and second motion vectors based on the minimized distortion cost;
• and
• code the plurality of partitioned units individually by using the corresponding refined first and second motion vectors;
• when the current block of pixels is not partitioned for motion vector refinement, the circuitry is further configured to:
• identify a pair of motion vectors for coding the current block of pixels, and
• code the current block of pixels by using the identified pair of motion vectors without refining the pair of motion vectors.