Motion vector precision in merge with motion vector difference mode

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• construct a merge candidate list for a current video unit of a video;
• generate a first motion vector from the merge candidate list;
• determine a motion vector difference offset based on a motion distance and a motion direction, wherein the motion distance is determined based on a motion distance index and a sample precision;
• determine, a motion vector difference (MVD) based on the motion vector difference offset;
• determine, a second motion vector based on the MVD and the first motion vector;
• and
• perform a conversion between the current video unit and a bitstream of the video based on the second motion vector;
• wherein a first flag in the bitstream indicates whether only integer sample precision is used for indicating the motion distance,
• wherein the first flag is included in the bitstream in a case that a merge mode with motion vector difference enablement flag indicates that the merge mode with motion vector difference is enabled,
• wherein an element in a first column of a motion distance table is a product of a factor and a corresponding element with a same motion distance index in a second column of the motion distance table, wherein the first column is used to derive the motion distance when the first flag indicate that only integer sample precision is used for indicating the motion distance, and the second column is used to derive the motion distance when the first flag indicates that not only integer sample precision is used for indicating the motion distance, wherein the factor is 4.

A non-transitory computer-readable storage medium storing instructions that cause a processor to:

• construct a merge candidate list for a current video unit of a video;
• generate a first motion vector from the merge candidate list;
• determine a motion vector difference offset based on a motion distance and a motion direction, wherein the motion distance is determined based on a motion distance index and a sample precision;
• determine, a motion vector difference (MVD) based on the motion vector difference offset;
• determine, a second motion vector based on the MVD and the first motion vector;
• and
• perform a conversion between the current video unit and a bitstream of the video based on the second motion vector;
• wherein a first flag in the bitstream indicates whether only integer sample precision is used for indicating the motion distance,
• wherein the first flag is included in the bitstream in a case that a merge mode with motion vector difference enablement flag indicates that the merge mode with motion vector difference is enabled,
• wherein an element in a first column of a motion distance table is a product of a factor and a corresponding element with a same motion distance index in a second column of the motion distance table, wherein the first column is used to derive the motion distance when the first flag indicate that only integer sample precision is used for indicating the motion distance, and the second column is used to derive the motion distance when the first flag indicates that not only integer sample precision is used for indicating the motion distance, wherein the factor is 4.

A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• constructing a merge candidate list for a current video unit of a video;
• generating a first motion vector from the merge candidate list;
• determining a motion vector difference offset based on a motion distance and a motion direction, wherein the motion distance is determined based on a motion distance index and a sample precision;
• determining, a motion vector difference (MVD) based on the motion vector difference offset;
• determining, a second motion vector based on the MVD and the first motion vector;
• and
• generating the bitstream based on the second motion vector;
• wherein a first flag in the bitstream indicates whether only integer sample precision is used for indicating the motion distance,
• wherein the first flag is included in the bitstream in a case that a merge mode with motion vector difference enablement flag indicates that the merge mode with motion vector difference is enabled,
• wherein an element in a first column of a motion distance table is a product of a factor and a corresponding element with a same motion distance index in a second column of the motion distance table, wherein the first column is used to derive the motion distance when the first flag indicate that only integer sample precision is used for indicating the motion distance, and the second column is used to derive the motion distance when the first flag indicates that not only integer sample precision is used for indicating the motion distance, wherein the factor is 4.