Method and apparatus of adaptive bi-prediction for video coding

A method, comprising:

• while using generalized bi-prediction (GBi):
• receiving input data associated with a current block in a current picture, wherein the input data comprises information associated with a block size of the current block;
• determining a set of weighting factor pairs, wherein a size of the set of weighting factor pairs depends on the block size of the current block;
• deriving a set of advanced motion vector prediction (AMVP) candidate lists comprising MVP (motion vector prediction) candidates;
• deriving a set of final motion information based on the MVP candidates;
• determining that the set of final information comprises a bi-prediction predictor;
• generating a final predictor by combining two reference blocks associated with the final motion information using a target weighting factor pair selected from the set of weighting factor pairs;
• and
• encoding or decoding the current block using the final predictor,
• wherein a size of the set of weighting factor pairs is one of at least a first size or a second size, wherein the first size is based on a first block size smaller than a threshold size, and the second size is based on a second block size greater than or equal to the threshold size, wherein the second size is larger than the first size.