Signaling of motion vector difference derivation

A video encoding method, comprising:

• receiving pixel data of a current coding unit (CU) of a current picture;
• determining whether the current CU is coded according to bi-directional prediction;
• and
• in a case that the current CU is determined to be coded according to the bi-directional prediction:
• determining a first motion vector difference for a first prediction direction of the bi-directional prediction;
• after the first motion vector difference is determined, determining a second motion vector difference for a second prediction direction of the bi-directional prediction, including:
• determining whether a first flag indicates the second motion vector difference being zero;
• in a case that the first flag is determined to indicate the second motion vector difference being zero, setting the second motion vector difference to a zero vector;
• in a case that the first flag is determined to not indicate the second motion vector difference being zero,
• setting the second motion vector difference to be at an opposite value of the first motion vector difference when a second flag has a first value, and
• determining the second motion vector difference when the second flag has a second value;
• and
• encoding the current CU according to the bi-directional prediction performed based on the first motion vector difference and the second motion vector difference.

An electronic apparatus, comprising:

• a video decoder circuit configured to perform operations comprising:
• receiving encoded data associated with a current coding unit (CU) of a current picture of a video;
• and
• determining, based on the encoded data, whether the current CU is coded according to bi-directional prediction;
• and
• in a case that the current CU is determined to be coded according to the bi-directional prediction, performing:
• determining a first motion vector difference for a first prediction direction of the bi-directional prediction:
• after the first motion vector difference is determined, determining a second motion vector difference for a second prediction direction of the bi-directional prediction, including:
• determining whether a first flag indicates the second motion vector difference being zero;
• in a case that the first flag is determined to indicate the second motion vector difference being zero, setting the second motion vector difference to a zero vector;
• in a case that the first flag is determined to not indicate the second motion vector difference being zero, setting the second motion vector difference to be an opposite value of the first motion vector difference when a second flag has a first value, and receiving the second motion vector difference from the encoded data when the second flag has a second value;
• and
• reconstructing the current CU according to the bi-directional prediction performed based on the first motion vector difference and the second motion vector difference.

A video coding method, comprising:

• receiving data to be encoded or decoded as a current coding unit (CU) of a current picture of a video;
• and
• determining, based on the received data, whether the current CU is coded according to bi-directional prediction;
• and
• in a case that the current CU is determined to be coded according to the bi-directional prediction, performing:
• determining a first motion vector difference for a first prediction direction of the bi-directional prediction;
• after the first motion vector difference is determined, determining a second motion vector difference for a second prediction direction of the bi-directional prediction, including
• determining whether a first flag indicates the second motion vector difference being zero;
• in a case that the first flag is determined to indicate the second motion vector difference being zero, setting the second motion vector difference to a zero vector;
• in a case that the first flag is detei lined to not indicate the second motion vector difference being zero,
• setting the second motion vector difference to be at an opposite value of the first motion vector difference when a second flag has a first value, and
• determining the second motion vector difference when the second flag has a second value;
• and
• encoding or decoding the current CU according to the bi-directional prediction performed based on the first motion vector difference and the second motion vector difference.