Method and apparatus of motion-vector rounding unification for video coding system

1. A method of video coding performed by a video encoder or a video decoder that utilizes an Inter coding tool, the method comprising:

receiving input data related to a current block in a current picture at a video encoder side or a video bitstream corresponding to compressed data including the current block at a video decoder side;

determining one or more MVs (motion vectors) associated with a target Inter coding tool for the current block at the video encoder side or at the video decoder side;

applying a same conversion process to said one or more MVs to generate one or more converted MVs at the video encoder side or at the video decoder side when the target Inter coding tool belongs to at least two tools of a group, wherein the group comprises at least one of inherited affine Merge candidate derivation and affine sub-block MV derivation, wherein the same conversion process comprises a specific rounding process, wherein the specific rounding process comprises rounding a value to a nearest integer value when there is only one nearest integer value, and rounding the value to an integer value when the value is midway between two integer values, regardless of whether the value is a positive or negative value, wherein the integer value comprises the one of the two integer values that is closer to zero; and

encoding the current block or motion information of the current block using said one more converted MVs at the video encoder side or decoding the current block or the motion information of the current block using said one or more converted MVs at the video decoder side.

2. The method of claim 1 , wherein the specific rounding process is implemented as MV_rounded=(MV+offset−(MV>=0))>> shift, wherein MV represents a target MV being applied the same conversion process, MV_rounded represents a converted target MV, shift represents an integer corresponding to a number of bits for a right-shift operation, offset is equal to (1<<(shift−1)), and “<<” represent a left-shift operation.

3. The method of claim 1 , wherein when the target Inter coding tool corresponds to inherited affine Merge candidate derivation, said one or more MVs corresponds to one or more affine control point MVs.

4. The method of claim 1 , wherein when the target Inter coding tool corresponds to affine sub-block MV derivation, said one or more MVs corresponds to one or more derived affine sub-block MVs.

5. The method of claim 1 , wherein rounding the value to the nearest integer value is performed only when there is only one nearest integer value.

6. The method of claim 1 , wherein the specific rounding process is implemented by adding an offset to a value corresponding to said one or more MVs before applying a right shift operation.

7. The method of claim 6 , wherein the offset is equal to (1<<(shift−1))−1, where “<<” represent a left-shift operation, and the shift represents an integer corresponding to a number of bits for the right shift operation.

8. An apparatus for video coding performed by a video encoder or a video decoder that utilizes an Inter coding tool, the apparatus comprising one or more electronic circuits or processors arranged to:

receive input data related to a current block in a current picture at a video encoder side or a video bitstream corresponding to compressed data including the current block at a video decoder side;

determine one or more MVs (motion vectors) associated with a target Inter coding tool for the current block at the video encoder side or at the video decoder side;

apply a same conversion process to said one or more MVs to generate one or more converted MVs at the video encoder side or at the video decoder side when the target Inter coding tool belongs to at least two tools of a group, wherein the group comprises at least one of inherited affine Merge candidate derivation and affine sub-block MV derivation, wherein the same conversion process comprises a specific rounding process, wherein the specific rounding process comprises rounding a value to a nearest integer value when there is only one nearest integer value, and rounding the value to an integer value when the value is midway between two integer values, regardless of whether the value is a positive or negative value, wherein the integer value comprises the one of the two integer values that is closer to zero; and

encode the current block or motion information of the current block using said one more converted MVs at the video encoder side or decode the current block or the motion information of the current block using said one or more converted MVs at the video decoder side.

9. The apparatus of claim 8 , wherein the specific rounding process is implemented as MV_rounded=(MV+offset−(MV>=0))>> shift, wherein MV represents a target MV being applied the same conversion process, MV_rounded represents a converted target MV, shift represents an integer corresponding to a number of bits for a right-shift operation, offset is equal to (1<<(shift−1)), and “<<” represent a left-shift operation.

10. The apparatus of claim 8 , wherein when the target Inter coding tool corresponds to inherited affine Merge candidate derivation, said one or more MVs corresponds to one or more affine control point MVs.

11. The apparatus of claim 8 , wherein when the target Inter coding tool corresponds to affine sub-block MV derivation, said one or more MVs corresponds to one or more derived affine sub-block MVs.

12. The apparatus of claim 8 , wherein the specific rounding process is implemented by adding an offset to a value corresponding to said one or more MVs before applying a right shift operation.

13. The apparatus of claim 12 , wherein the offset is equal to (1<<(shift−1))−1, where “<<” represent a left-shift operation, and the shift represents an integer corresponding to a number of bits for the right shift operation.