Motion vector decoding method and decoder

A decoder, comprising:

• a non-transitory memory having processor-executable instructions stored thereon;
• and
• a processor, coupled to the non-transitory memory, configured to execute the processor-executable instructions to facilitate:
• determining a prediction motion vector of a to-be-decoded unit based on a motion vector of a prediction unit of the to-be-decoded unit;
• when a face image in which the to-be-decoded unit is located and at least one of a face image in which a first reference unit is located and a face image in which the prediction unit is located are not face images in a same orientation, performing a first update on the prediction motion vector, wherein the first update is used to determine a mapping vector that is of the prediction motion vector and that is in a plane of the face image in which the to-be-decoded unit is located, the first reference unit is determined based on the motion vector of the prediction unit and a reference image identifier of the prediction unit, the face image is a planar mapping image of a panorama image in an orientation, M face images form a closed M-hedron, a centroid of the M-hedron coincides with a centroid of an object using the panorama image as a surface, a line connecting the centroid of the M-hedron to a first position point on the face image intersects the panorama image at a second position point, the first position point is a mapping point of the second position point, and M is greater than or equal to 4;
• and
• obtaining a motion vector of the to-be-decoded unit based on the prediction motion vector obtained after the first update.