Method and apparatus for video coding using inter-prediction mode signaling to dertermine motion vectors

1. A method for video decoding in a processor, comprising:

decoding, by processing circuitry, prediction information of a current block in a current picture from a coded video bitstream, the prediction information being indicative of an inter prediction mode that signals a value associated with a motion vector difference in the coded video bitstream;

setting, by the processing circuitry, a precision to be used to convert the signaled value in the coded bitstream to the motion vector difference, based on a size of the current block; and

converting, by the processing circuitry, the signaled value in the coded video bitstream to the motion vector difference based on the set precision so that the motion vector difference has the set precision;

determining, by the processing circuitry, a motion vector based on a prediction of the motion vector and the motion vector difference: and

reconstructing, by the processing circuitry, at least a sample of the current block according to the determined motion vector.

2. The method of claim 1 , further comprising:

decoding, by the processing circuitry, at least a flag indicative of the precision for the motion vector difference used in an affine mode according to a context that is selected based on the size of the current block.

3. The method of claim 2 , further comprising at least one of:

selecting the context based on a comparison of a number of luma samples in the current block to a first threshold;

selecting the context based on a comparison of a larger value of a width and a height of the current block to a second threshold; and

selecting the context based on a comparison of a smaller value of the width and the height of the current block to a third threshold.

4. The method of claim 1 , further comprising:

decoding, by the processing circuitry, a flag indicating whether a specific precision is used based on a context that is shared in an affine mode and a non-affine mode.

5. The method of claim 1 , further comprising:

determining, by the processing circuitry, the precision for the motion vector difference based on a predetermined relationship that associates sizes with precisions.

6. The method of claim 1 , further comprising:

decoding a switch bin, which indicates that the precision for the motion vector difference is a block size dependent precision.

7. The method of claim 6 , wherein the switch bin is used to switch between the block size dependent precision and at least one of:

a default precision; and

a selected precision that is selected from a set of fixed precisions based on an index.

8. The method of claim 1 , further comprising:

applying the precision to a first motion vector difference of a first control point in an affine mode; and

applying a fixed precision to a second motion vector difference of a second control point.

9. An apparatus for video decoding, comprising:

processing circuitry configured to:

decode prediction information of a current block in a current picture from a coded video bitstream, the prediction information being indicative of an inter prediction mode that signals a value associated with a motion vector difference in the coded video bitstream;

set a precision to be used to convert the signaled value in the coded bitstream to the motion vector difference, based on a size of the current block; and

convert the signaled value in the coded video bitstream to the motion vector difference based on the set precision so that the motion vector difference has the set precision;

determine a motion vector based on a prediction of the motion vector and the motion vector difference; and

reconstruct at least a sample of the current block according to the determined motion vector.

10. The apparatus of claim 9 , wherein the processing circuitry is further configured to:

decode at least a flag indicative of the precision for the motion vector difference used in an affine mode according to a context that is selected based on the size of the current block.

11. The apparatus of claim 10 , wherein the processing circuitry is further configured to select the context based on at least one of:

a comparison of a number of luma samples in the current block to a first threshold;

a comparison of a larger value of a width and a height of the current block to a second threshold; and

a comparison of a smaller value of the width and the height of the current block to a third threshold.

12. The apparatus of claim 9 , wherein the processing circuitry is further configured to:

decode a flag for indicating whether a specific precision is used based on a context that is shared in an affine mode and a non-affine mode.

13. The apparatus of claim 9 , wherein the processing circuitry is further configured to:

determine the precision for the motion vector difference based on a predetermined relationship that associates sizes with precisions.

14. The apparatus of claim 9 , wherein the processing circuitry is further configured to:

decode a switch bin, which indicates that the precision for the motion vector difference is a block size dependent precision.

15. The apparatus of claim 14 , wherein the switch is used to switch between the block size dependent precision and at least one of:

a default precision; and

a selected precision that is selected from a set of fixed precisions based on an index.

16. The apparatus of claim 9 , wherein the processing circuitry is further configured to:

apply the precision to a first motion vector difference of a first control point in an affine mode; and

apply a fixed precision to a second motion vector difference of a second control point.

17. A method for video decoding in a processor, comprising:

decoding prediction information of a current block in a current picture from a coded video bitstream, the prediction information being indicative of an inter prediction mode that signals a value associated with a motion vector difference in the coded video bitstream;

decoding a switch bin, which indicates that a precision for the motion vector difference is a block size dependent precision;

determining the precision for the motion vector difference based on a size of the current block;

converting the signaled value in the coded video bitstream to the motion vector difference based on the determined precision;

determining the motion vector based on a prediction of the motion vector and the motion vector difference; and

reconstructing at least a sample of the current block according to the motion vector.