Rounding of motion vectors for adaptive motion vector difference resolution and increased motion vector storage precision in video coding

A video coding device comprising:

• a memory configured to store video data;
• and
• one or more processing units implemented in circuitry and configured to:
• code a value of a motion vector difference for a current block of video data;
• obtain, from a motion vector buffer, a value of a motion vector predictor for the current block of video data;
• obtain a shift value that is based on a resolution of the value of the motion vector difference and based on a storage resolution shift amount for motion vectors;
• round, based on the shift value, the value of the motion vector predictor obtained from the motion vector buffer directly to the resolution of the value of the motion vector difference, wherein, to round the value of the motion vector predictor, the one or more processing units are configured to:
• right-shift, by the shift value, a value representing a sum of the value of the motion vector predictor obtained from the motion vector buffer and a rounding offset and
• left-shift, by the shift value, the right-shifted value representing the sum of the motion vector predictor and the rounding offset to obtain the rounded value of the motion vector predictor;
• add the rounded value of the motion vector predictor to the value of the motion vector difference to obtain a value of a motion vector for the current block;
• obtain, based on the value of the motion vector for the current block, samples of a predictor block for the current block;
• and
• reconstruct samples of the current block based on the samples of the predictor block for the current block.

A non-transitory computer-readable storage medium storing instructions that, when executed, cause one or more processors to:

• code a value of a motion vector difference for a current block of video data;
• obtain, from a motion vector buffer, a value of a motion vector predictor for the current block of video data;
• obtain a shift value that is based on a resolution of the value of the motion vector difference and based on a storage resolution shift amount for motion vectors;
• round, based on the shift value, the value of the motion vector predictor obtained from the motion vector buffer directly to the resolution of the value of the motion vector difference, wherein the instructions that cause the one or more processors to round the value of the motion vector predictor comprise instructions that cause the one or more processors to:
• right-shift, by the shift value, a value representing a sum of the value of the motion vector predictor obtained from the motion vector buffer and a rounding offset and
• left-shift, by the shift value, the right-shifted value representing the sum of the motion vector predictor and the rounding offset to obtain the rounded value of the motion vector predictor;
• add the rounded value of the motion vector predictor to the value of the motion vector difference to obtain a value of a motion vector for the current block;
• obtain, based on the value of the motion vector for the current block, samples of a predictor block for the current block;
• and
• reconstruct samples of the current block based on the samples of the predictor block for the current block.