Method and apparatus of improved merge with motion vector difference for video coding
A prediction method and apparatus for video coding include a set of Merge candidates having an MMVD (Merge mode with motion vector differences (MVD)) candidate are generated. When the current block has a block size belonging to at least one default block size, whether a target candidate in the set of Merge candidates is bi-prediction is determined after the set of Merge candidates is generated. If the target candidate is bi-prediction: the target candidate is replaced by a uni-prediction candidate; the uni-prediction candidate is included in the set of Merge candidates to generate a modified set of Merge candidates; and current motion information associated with the current block is encoded using the modified set of Merge candidates at the video encoder side or the current motion information associated with the current block is decoded at the video decoder side using the modified set of Merge candidates.
1. A method of prediction for video coding, 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 in the current picture at a video decoder side;
generating a set of Merge candidates comprising an MMVD (Merge mode with motion vector differences (MVD)) candidate, wherein the MMVD candidate is derived by determining a base candidate and modifying one or more parts of MV (Motion Vector) expression of the base candidate to generate the MMVD candidate;
if the current block has a block size belonging to at least one default block size and a target candidate in the set of Merge candidates is bi-prediction after the set of Merge candidates is generated:
replacing the target candidate by a uni-prediction candidate; and
encoding current motion information associated with the current block using the uni-prediction candidate at the video encoder side or decoding the current motion information associated with the current block using the uni-prediction candidate at the video decoder side.
2. The method of claim 1 , wherein the at least one default block size comprises 4×4.
3. The method of claim 1 , wherein the set of Merge candidates further comprises a normal Merge candidate or a pairwise average Merge candidate.
4. The method of claim 1 , wherein the set of Merge candidates further comprises a history-based Merge candidate.
5. The method of claim 1 , wherein the base candidate is only selected from first Merge candidates in the set of Merge candidates with a default Merge type.
6. The method of claim 5 , wherein if none of the set of Merge candidates has the default Merge type, a default MV is included in modified set of Merge candidates.
7. The method of claim 6 , wherein the default MV is referred from a reference picture in reference picture List 0 .
8. The method of claim 1 , wherein said one or more parts of MV expression comprise prediction direction information, starting point, motion magnitude, motion direction, or a combination thereof associated with the MV expression.
9. An apparatus of Inter prediction for video coding, the apparatus of Inter prediction for video coding 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 in the current picture at a video decoder side;
generate a set of Merge candidates comprising an MMVD (Merge mode with motion vector differences (MVD)) candidate, wherein the MMVD candidate is derived by determining a base candidate and modifying one or more parts of MV (Motion Vector) expression of the base candidate to generate the MMVD candidate;
if the current block has a block size belonging to at least one default block and a target candidate in the set of Merge candidates is bi-prediction after the set of Merge candidates is generated:
replace the target candidate by a uni-prediction candidate; and
encode current motion information associated with the current block using the uni-prediction candidate at the video encoder side or decode the current motion information associated with the current block using the uni-prediction candidate at the video decoder side.