Restrictions on motion vector difference

1. A method of processing video data, comprising:

determining, for a conversion between a first block of a video and a bitstream of the video, a motion vector (MV) component and a motion vector difference (MVD) component associated with the first block; and

performing the conversion based on a constrained MVD component,

wherein a range of the MV component associated with the first block is [−2 M , 2 M −1], where M=K+L, in which K denotes the number of bits used to represent an integer part of the MV component, and L denotes the number of bits used to represent a fractional part of the MV component, wherein the MV component is represented in ½ L -luma-sample precision,

wherein a value of the MVD component is constrained to be in a range of MVD component, wherein the range of MVD component is [−2 M , 2 M −1], and

wherein M=17, K and L are positive integers.

2. The method of claim 1 , wherein the range is adapted to an allowable MVD precision and/or allowable motion vector (MV) precision of a codec.

3. The method of claim 2 , wherein the allowable MVD precision and/or allowable motion vector (MV) precision is 1/16-luma-sample precision.

4. The method of claim 1 , wherein when there are multiple allowable MVD precisions and/or MV precisions in the codec, the range of MVD component is adapted to a finest precision of the multiple allowable MVD precisions and/or MV precisions.

5. The method of claim 4 , wherein when the multiple allowable MVD precisions and/or MV precisions include 1/16-luma-sample, ¼-luma-sample and 1-luma-sample, the range of MVD component is adapted to the 1/16-luma-sample precision.

6. The method of claim 5 , wherein the first block is applied with a first coding mode in which a motion information is derived based on a motion vector candidate list and a scaled MVD, and

wherein the scaled MVD is generating by bit-shifting the MVD, and the motion vector candidate list includes inherited candidates derived from neighboring blocks coded with first coding mode, constructed candidates and candidates with zero MVs.

7. The method of claim 1 , wherein K further denotes the number of bits used to represent an integer part of the MVD component, and L further denotes the number of bits used to represent a fractional part of the MVD component, wherein the MVD component is represented in ½ L -luma-sample precision.

8. The method of claim 7 , wherein K=13, and L=4.

9. The method of claim 1 , wherein the MVD component is a signaled MVD component coded in a bitstream, or a converted MVD component associated with to a certain precision through an internal shifting operation in decoding process.

10. The method of claim 1 , wherein the MVD component includes a horizontal MVD component and a vertical MVD component, and the horizontal MVD component and the vertical MVD component have the same range.

11. The method of claim 1 , wherein the MVD component is represented by integral bits, fractional bits, and a sign bit.

12. The method of claim 1 , wherein the range of an MV associated with the first block is same as the range of MVD component.

13. The method of claim 1 , wherein the conversion includes decoding the first block from the bitstream.

14. The method of claim 1 , wherein the conversion includes encoding the first block into the bitstream.

15. 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:

determine, for a conversion between a first block of a video and a bitstream of the video, a motion vector (MV) component and a motion vector difference (MVD) component associated with the first block; and

perform the conversion based on a constrained MVD component,

wherein a range of the MV component associated with the first block is [−2 M , 2 M −1], where M=K+L, in which K denotes the number of bits used to represent an integer part of the MV component, and L denotes the number of bits used to represent a fractional part of the MV component, wherein the MV component is represented in ½ L -luma-sample precision,

wherein a value of the MVD component is constrained to be in a range of MVD component, wherein the range of MVD component is [−2 M , 2 M −1], and

wherein M=17, K and L are positive integers.

16. The apparatus of claim 15 , wherein the range is adapted to an allowable MVD precision and/or allowable motion vector (MV) precision of a codec.

17. The apparatus of claim 16 , wherein the allowable MVD precision and/or allowable motion vector (MV) precision is 1/16-luma-sample precision.

18. The apparatus of claim 15 , wherein when there are multiple allowable MVD precisions and/or MV precisions in the codec, the range of MVD component is adapted to a finest precision of the multiple allowable MVD precisions and/or MV precisions.

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

determine, for a conversion between a first block of a video and a bitstream of the video, a motion vector (MV) component and a motion vector difference (MVD) component associated with the first block; and

perform the conversion based on a constrained MVD component,

wherein a range of the MV component associated with the first block is [−2 M , 2 M −1], where M=K+L, in which K denotes the number of bits used to represent an integer part of the MV component, and L denotes the number of bits used to represent a fractional part of the MV component, wherein the MV component is represented in ½ L -luma-sample precision,

wherein a value of the MVD component is constrained to be in a range of MVD component, wherein the range of MVD component is [−2 M , 2 M −1], and

wherein M=17, K and L are positive integers.

20. A method for storing a bitstream of a video, comprising:

determining, a first block of the video, a motion vector (MV) component and a motion vector difference (MVD) component associated with the first block;

generating the bitstream based on a constrained MVD component; and

storing the bitstream in a non transitory computer readable recording medium,

wherein a range of the MV component associated with the first block is [−2 M , 2 M −1], where M=K+L, in which K denotes the number of bits used to represent an integer part of the MV component, and L denotes the number of bits used to represent a fractional part of the MV component, wherein the MV component is represented in ½ L -luma-sample precision,

wherein a value of the MVD component is constrained to be in a range of MVD component, wherein the range of MVD component is [−2 M , 2 M −1], and

wherein M=17, K and L are positive integers.