Method and apparatus of motion refinement for video coding

1. A method of video coding using Pattern-based MV derivation (PMVD) or Decoder-side MV refinement (DMVR) to refine motion for a bi-direction predicted block, the method comprising:

receiving input data associated with a current block in a current picture, wherein the current block is coded using bi-direction prediction;

determining a first motion-compensated reference block associated with the current block in a first reference picture from a reference picture list 0, wherein the first motion-compensated reference block includes additional surrounding first pixels around a first corresponding block of the current block in the first reference picture for performing interpolation filtering required for any fractional motion vector of the current block;

determining a second motion-compensated reference block associated with the current block in a second reference picture from a reference picture list 1, wherein the second motion-compensated reference block includes additional surrounding second pixels around a second corresponding block of the current block in the second reference picture for performing interpolation filtering required for any fractional motion vector of the current block;

applying a PMVD process or a DMVR process to generate motion refinement for the current block using reference data corresponding to the first motion-compensated reference block and the second motion-compensated reference block without other reference data outside the first motion-compensated reference block and the second motion-compensated reference block; and

encoding or decoding the current block based on motion-compensated prediction according to the motion refinement,

wherein the PMVD process, the DMVR process, or the motion-compensated prediction comprises:

in response to applying a filter that refers to samples having a first portion of the samples within the first motion-compensated reference block and the second motion-compensated reference block and a second portion of the samples outside the first motion-compensated reference block and the second motion-compensated reference block,

generating padded samples according to the first portion of the samples, and

applying the filter according to the first portion of the samples and the padded samples without using the second portion of the samples.

2. The method of claim 1 , wherein the padded samples are generated by extending boundary pixels of the first portion of the samples.

3. The method of claim 1 , wherein the padded samples are generated by mirroring boundary pixels of the first portion of the samples.

4. An apparatus of video coding using Pattern-based MV derivation (PMVD) or Decoder-side MV refinement (DMVR) to refine motion for a bi-direction predicted block, the apparatus of video coding comprising one or more electronic circuits or processors configured to:

receive input data associated with a current block in a current picture, wherein the current block is coded using bi-direction prediction;

determine a first motion-compensated reference block associated with the current block in a first reference picture from a reference picture list 0, wherein the first motion-compensated reference block includes additional surrounding first pixels around a first corresponding block of the current block in the first reference picture for performing interpolation filtering required for any fractional motion vector of the current block;

determine a second motion-compensated reference block associated with the current block in a second reference picture from a reference picture list 1, wherein the second motion-compensated reference block includes additional surrounding second pixels around a second corresponding block of the current block in the second reference picture for performing interpolation filtering required for any fractional motion vector of the current block;

apply a PMVD process or a DMVR process to generate motion refinement for the current block using reference data corresponding to the first motion-compensated reference block and the second motion-compensated reference block without other reference data outside the first motion-compensated reference block and the second motion-compensated reference block; and

encode or decode the current block based on motion-compensated prediction according to the motion refinement,

wherein the one or more electronic circuits or processors are configured to apply the PMVD process, the DMVR process, or the motion-compensated prediction by performing at least:

in response to applying a filter that refers to samples having a first portion of the samples within the first motion-compensated reference block and the second motion-compensated reference block and a second portion of the samples outside the first motion-compensated reference block and the second motion-compensated reference block,

generating added samples according to the first portion of the samples, and

applying the filter according to the first portion of the samples and the padded samples without using the second portion of the samples.

5. The apparatus of claim 4 , wherein the padded samples are generated by extending boundary pixels of the first portion of the samples.

6. The apparatus of claim 4 , wherein the padded samples are generated by mirroring boundary pixels of the first portion of the samples.

7. A non-transitory computer readable medium storing program instructions causing a processing circuit of an apparatus to perform a video coding method, and the method comprising:

receiving input data associated with a current block in a current picture, wherein the current block is coded using bi-direction prediction;

determining a first motion-compensated reference block associated with the current block in a first reference picture from a reference picture list 0, wherein the first motion-compensated reference block includes additional surrounding first pixels around a first corresponding block of the current block in the first reference picture for performing interpolation filtering required for any fractional motion vector of the current block;

determining a second motion-compensated reference block associated with the current block in a second reference picture from a reference picture list 1, wherein the second motion-compensated reference block includes additional surrounding second pixels around a second corresponding block of the current block in the second reference picture for performing interpolation filtering required for any fractional motion vector of the current block;

applying a Pattern-based MV derivation (PMVD) process or a Decoder-side MV refinement (DMVR) process to generate motion refinement for the current block using reference data corresponding to the first motion-compensated reference block and the second motion-compensated reference block without other reference data outside the first motion-compensated reference block and the second motion-compensated reference block; and

encoding or decoding the current block based on motion-compensated prediction according to the motion refinement,

wherein the PMVD process, the DMVR process, or the motion-compensated prediction comprises:

in response to applying a filter that refers to samples having a first portion of the samples within the first motion-compensated reference block and the second motion-compensated reference block and a second portion of the samples outside the first motion-compensated reference block and the second motion-compensated reference block,

generating padded samples according to the first portion of the samples, and

applying the filter according to the first portion of the samples and the padded samples without using the second portion of the samples.

8. The non-transitory computer readable medium of claim 7 , wherein the padded samples are generated by extending boundary pixels of the first portion of the samples.

9. The non-transitory computer readable medium of claim 7 , wherein the padded samples are generated by mirroring boundary pixels of the first portion of the samples.