Rules on updating luts

1. A method for video processing, comprising:

performing a conversion between video blocks of a video and a bitstream of the video and maintaining one or more tables of motion candidates during the conversion;

wherein the performing a conversion comprises:

constructing a motion candidate list for a current video block of the video, wherein a suitability of the one or more tables is based on a coding characteristic of the current video block, wherein the suitability indicates whether to use the one or more tables during the constructing, wherein the one or more tables comprise motion candidates associated with processing at least one video block received prior to the current video block, and wherein using the one or more tables comprises checking at least one motion candidate of the one or more tables to determine whether to add the checked motion candidate to the motion candidate list;

performing the conversion between the current video block and the bitstream of the video based on the motion candidate list; and

selectively using a motion candidate associated with motion information of the current video block to update the one or more tables, wherein whether to update the one or more tables is based on the coding characteristic, wherein, in a case that the one or more tables are not used based on the coding characteristic, updating of the one or more tables with the motion information of the current video block is skipped based on the coding characteristic, and wherein the coding characteristic comprises a coding mode of the current video block.

2. The method of claim 1 , wherein the performing a conversion comprises:

encoding the current video block into the bitstream.

3. The method of claim 1 , wherein the performing a conversion comprises:

decoding the current video block from the bitstream.

4. The method of claim 1 , wherein the coding characteristic further comprises a size of the current video block.

5. The method of claim 1 , wherein the coding characteristic indicates that the coding mode of the current video block is one of an affine mode, an intra mode, an affine merge mode, or an affine Advanced Motion Vector Prediction (AMVP) mode.

6. The method of claim 1 , wherein in case that the one or more tables are used based on the coding characteristic, updating of the one or more tables with the motion information of the current video block is performed based on the coding characteristic.

7. The method of claim 6 , wherein the coding characteristic indicates that the coding mode of the current video block is one of a merge mode which is a non-affine merger mode, or an AMVP mode which is a non-affine AMVP mode.

8. The method of claim 1 , wherein in case that the one or more tables are used based on the coding characteristic, updating of the one or more tables with the motion information of the current video block is skipped based on the coding characteristic.

9. The method of claim 8 , wherein the coding characteristic indicates that the coding mode of the current video block is a triangular prediction mode.

10. The method of claim 1 , wherein in case that the one or more tables are not used based on the coding characteristic, updating of the one or more tables with the motion information of the current video block is performed based on the coding characteristic.

11. The method of claim 1 , wherein there is a possibility not to update the one or more tables using the motion information of a first block if the one or more tables are used during constructing the candidate list.

12. The method of claim 1 , wherein there is a possibility to update the one or more tables using the motion information of a first block if the one or more tables are not used during constructing the candidate list.

13. The method of claim 1 , wherein the one or more tables are used based on the coding mode of the current video block belonging to at least one first coding mode, wherein the at least one first coding mode comprises at least one of a merge mode which is a non-affine merge mode, an Advanced Motion Vector Prediction (AMVP) mode which is a non-affine AMVP mode, an inter coding mode.

14. The method of claim 1 , wherein the one or more tables are not used based on the coding mode of the current video block belonging to at least one second coding mode, wherein the at least one second coding mode comprises at least one of: an intra mode, an affine mode, an affine AMVP mode, an affine merge mode, a sub-block based mode.

15. The method of claim 1 , wherein the updating of the one or more tables comprises:

comparing a motion candidate associated with the current video block with a number of entries in the one or more tables; and

updating the one or more tables based on the comparing.

16. The method of claim 15 , wherein the number of entries correspond to last m entries in one of the one or more tables.

17. The method of claim 15 , wherein the updating comprises adding the motion candidates as a last entry of one of the one or more tables.

18. The method of claim 15 , wherein the one or more tables include no duplicated entries.

19. The method of claim 1 , wherein a motion candidate in the one or more tables are associated with motion information including at least one of: a prediction direction, a reference picture index, motion vector values, an intensity compensation flag, an affine flag, a motion vector difference precision, a filter parameter used in a filtering process, or a motion vector difference value.

20. 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:

performing a conversion between video blocks of a video and a bitstream of the video and maintaining one or more tables of motion candidates during the conversion;

wherein the performing a conversion comprises:

constructing a motion candidate list for a current video block of the video, wherein a suitability of the one or more tables is based on a coding characteristic of the current video block, wherein the suitability indicates whether to use the one or more tables during the constructing, wherein the one or more tables comprise motion candidates associated with processing at least one video block received prior to the current video block, and wherein using the one or more tables comprises checking at least one motion candidate of the one or more tables to determine whether to add the checked motion candidate to the motion candidate list;

performing the conversion between the current video block and the bitstream of the video based on the motion candidate list; and

selectively using a motion candidate associated with motion information of the current video block to update the one or more tables, wherein whether to update the one or more tables is based on the coding characteristic, wherein, in a case that the one or more tables are not used based on the coding characteristic, updating of the one or more tables with the motion information of the current video block is skipped based on the coding characteristic, and wherein the coding characteristic comprises a coding mode of the current video block.

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

performing a conversion between video blocks of a video and a bitstream of the video and maintaining one or more tables of motion candidates during the conversion;

wherein the performing a conversion comprises:

constructing a motion candidate list for a current video block of the video, wherein a suitability of the one or more tables is based on a coding characteristic of the current video block, wherein the suitability indicates whether to use the one or more tables during the constructing, wherein the one or more tables comprise motion candidates associated with processing at least one video block received prior to the current video block, and wherein using the one or more tables comprises checking at least one motion candidate of the one or more tables to determine whether to add the checked motion candidate to the motion candidate list;

performing the conversion between the current video block and the bitstream of the video based on the motion candidate list; and

selectively using a motion candidate associated with motion information of the current video block to update the one or more tables, wherein whether to update the one or more tables is based on the coding characteristic, wherein, in a case that the one or more tables are not used based on the coding characteristic, updating of the one or more tables with the motion information of the current video block is skipped based on the coding characteristic, and wherein the coding characteristic comprises a coding mode of the current video block.

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

performing a conversion between video blocks of a video and a bitstream-of the video and maintaining one or more tables of motion candidates during the conversion;

wherein the performing a conversion comprises:

constructing a motion candidate list for a current video block of the video, wherein a suitability of the one or more tables is based on a coding characteristic of the current video block, wherein the suitability indicates whether to use the one or more tables during the constructing, wherein the one or more tables comprise motion candidates associated with processing at least one video block received prior to the current video block, and wherein using the one or more tables comprises checking at least one motion candidate of the one or more tables to determine whether to add the checked motion candidate to the motion candidate list;

performing the conversion between the current video block and the bitstream of the video based on the motion candidate list; and

selectively using a motion candidate associated with motion information of the current video block to update the one or more tables, wherein whether to update the one or more tables is based on the coding characteristic, wherein, in a case that the one or more tables are not used based on the coding characteristic, updating of the one or more tables with the motion information of the current video block is skipped based on the coding characteristic, and wherein the coding characteristic comprises a coding mode of the current video block.