Method and apparatus for sub-block based temporal motion vector prediction

A video decoder for video decoding, comprising:

• processing circuitry configured to:
• acquire a current picture from a coded video bitstream,
• identify, for a current block included in the current picture, a reference block included in a reference picture, the reference picture being different from the current picture, the current block being divided into a first plurality of sub-blocks (CBSBs) that are coded in an inter mode, the reference block having a second plurality of sub-blocks (RBSBs), each CBSB corresponding to at least one RBSB,
• for each CBSB, in response to a corresponding RBSB being coded in an intra mode or intra block copy mode, set a first motion vector predictor of the corresponding CBSB to a default motion vector predictor, the default motion vector predictor being a zero motion vector,
• for each CBSB, in response to a corresponding RBSB being coded in an inter mode, set the first motion vector predictor of the corresponding CBSB using a second motion vector predictor of the corresponding RBSB as the first motion vector predictor of the corresponding CBSB, and
• decode each CBSB by performing sub-block based temporal motion vector prediction on each CBSB based on the first motion vector predictor for each CBSB.

A non-transitory computer readable medium having instructions stored therein, which when executed by a processor in a video decoder causes the processor to execute a method comprising:

• acquiring a current picture from a coded video bitstream;
• identifying, for a current block included in the current picture, a reference block included in a reference picture, the reference picture being different from the current picture, the current block being divided into a first plurality of sub-blocks (CBSBs) that are coded in an inter mode, the reference block having a second plurality of sub-blocks (RBSBs), each CBSB corresponding to at least one RBSB;
• for each CBSB, in response to a corresponding RBSB being coded in an intra mode or intra block copy mode, setting a first motion vector predictor of the corresponding CBSB to a default motion vector predictor, the default motion vector predictor being a zero motion vector;
• for each CBSB, in response to a corresponding RBSB being coded in an inter mode, setting the first motion vector predictor of the corresponding CBSB using a second motion vector predictor of the corresponding RBSB as the first motion vector predictor of the corresponding CBSB;
• and
• decoding each CBSB by performing sub-block based temporal motion vector prediction on each CBSB based on the first motion vector predictor for each CBSB.