Early termination for optical flow refinement

An encoder comprising:

• a memory configured to store instructions;
• and
• a processor coupled to the memory, wherein the instructions when executed cause the processor to be configured for:
• obtaining a pair of initial motion vectors for a current block, wherein the current block is a sub-block;
• obtaining two first prediction blocks for the current block based on the pair of initial motion vectors;
• calculating a first matching cost according to the two first prediction blocks, wherein the first matching cost is a sum of absolute differences (SAD) between the two first prediction blocks;
• obtaining a pair of refined motion vectors based on the pair of initial motion vectors;
• obtaining two second prediction blocks for the current block according to the pair of refined motion vectors;
• obtaining a second matching cost corresponding to the two second prediction blocks;
• determining whether an optical flow refinement process is to be performed or not, according to at least one preset condition, the at least one preset condition comprising a condition of whether the second matching cost is less than a threshold;
• performing an optical flow refinement process on the two second prediction blocks for obtaining a final prediction block for the current block, when it is determined that the optical flow refinement process is to be performed;
• obtaining the final prediction block by a weighted sum of the two second prediction blocks when it is determined that the optical flow refinement process is not to be performed;
• obtaining a residual block based on the current block and the final prediction block;
• and
• encoding the residual block into a bitstream.

A device for storing a bitstream, comprising a receiver and a memory, wherein the receiver is configured to receive one or more bitstreams, wherein the memory is configured to store the one or more bitstreams, wherein the one or more bitstreams are obtained by performing an encoding process on picture data, and the one or more bitstreams comprise encoded picture data and indication information for initial motion vectors, wherein the encoding process comprising:

• obtaining a pair of initial motion vectors for a current block, wherein the current block is a sub-block;
• obtaining two first prediction blocks for the current block based on the pair of initial motion vectors;
• calculating a first matching cost according to the two first prediction blocks, wherein the first matching cost is a sum of absolute differences (SAD) between the two first prediction blocks;
• obtaining a pair of refined motion vectors based on the pair of initial motion vectors;
• obtaining two second prediction blocks for the current block according to the pair of refined motion vectors;
• obtaining a second matching cost corresponding to the two second prediction blocks;
• determining whether an optical flow refinement process is to be performed or not, according to at least one preset condition, the at least one preset condition comprising a condition of whether the second matching cost is less than a threshold;
• performing an optical flow refinement process on the two second prediction blocks for obtaining a final prediction block for the current block, when it is determined that the optical flow refinement process is to be performed;
• obtaining the final prediction block by a weighted sum of the two second prediction blocks when it is determined that the optical flow refinement process is not to be performed;
• obtaining a residual block based on the current block and the final prediction block;
• and
• encoding the residual block into the bitstream.