Chain-based motion vector and chain-based motion vector predictor derivation

A method for video encoding, the method comprising:

• determining whether a current intermediate vector pointing to a first block in a first reference picture from a second block in a second reference picture is valid for use in deriving one of a chain-based motion vector (MV) and a chain-based motion vector predictor (MVP) for a current block in a current picture based on one or more of (i) first reference picture information of the first reference picture, (ii) current reference picture information of the current block, (iii) a position of the first block, and (iv) history information associated with at least one previously derived intermediate vector that is associated with the current block in the current picture and the second block in the second reference picture;
• when the current intermediate vector is determined to be valid,
• determining the one of the chain-based MV and the chain-based MVP for the current block based on the current intermediate vector and the at least one previously derived intermediate vector;
• and
• encoding the current block based on the one of the chain-based MV and the chain-based MVP using inter prediction, and
• encoding, in a video bitstream, coded information of the current block indicating that the current block is encoded using the inter prediction.

A method of processing visual media data, the method comprising:

• processing a video bitstream of the visual media data according to a format rule, wherein
• the bitstream includes coded information of a current block in a current picture indicating that the current block is decoded using inter prediction;
• and
• the format rule specifies that:
• whether a current intermediate vector pointing to a first block in a first reference picture from a second block in a second reference picture is valid for use in deriving one of a chain-based motion vector (MV) and a chain-based motion vector predictor (MVP) for the current block is determined based on one or more of (i) first reference picture information of the first reference picture, (ii) current reference picture information of the current block, (iii) a position of the first block, and (iv) history information associated with at least one previously derived intermediate vector that is associated with the current block in the current picture and the second block in the second reference picture, and
• when the current intermediate vector is determined to be valid,
• the one of the chain-based MV and the chain-based MVP for the current block is determined based on the current intermediate vector and the at least one previously derived intermediate vector;
• and
• the current block is reconstructed based on the one of the chain-based MV and the chain-based MVP.