Methods for sub-block based temporal motion vector prediction

A method of video encoding for an encoder, the method comprising:

• acquiring a current picture from a video sequence to be encoded;
• 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 to be 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, when a corresponding RBSB is 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, when a corresponding RBSB is 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
• encoding, in a coded video bitstream, each CBSB by performing sub-block based temporal motion vector prediction on each CBSB using the first motion vector predictor for each CBSB.

A non-transitory computer-readable storage medium storing instructions which, when executed by a processor, cause the processor to perform a method of encoding a bitstream comprising:

• acquiring a current picture from a video sequence to be encoded;
• 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, when a corresponding RBSB is 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, when a corresponding RBSB is 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;
• encoding each CBSB in the bitstream by performing sub-block based temporal motion vector prediction on each CBSB based on the first motion vector predictor for each CBSB;
• and
• transmitting the encoded bitstream.