Interaction between merge list construction and other tools

1. A method for video processing, comprising:

determining, based on a first threshold (T1), a maximum number of history-based motion vector prediction (HMVP) candidates in an HMVP table to be checked, wherein the HMVP table includes one or more HMVP candidates, and wherein the one or more checked HMVP candidates in the HMVP table are used for constructing a motion candidates list;

making a decision regarding a selective checking of a number of the HMVP candidates in the HMVP table in an order, the number of the HMVP candidates in the HMVP table checked not exceeding the maximum number of HMVP candidates to be checked;

constructing, based on the decision, the motion candidates list; and

performing, based on the motion candidates list, a conversion between a current block of a video and a bitstream of the video,

wherein checking the HMVP candidates in the HMVP table is terminated upon a determination that a number of available motion candidates in the motion candidates list, including added HMVP candidates, has reached a maximally allowed number of motion candidates in the motion candidates list minus a second threshold (T2), and wherein T2 is based on a coding mode of the current block.

2. The method of claim 1 , wherein the maximum number of HMVP candidates to be checked is equal to the first threshold.

3. The method of claim 1 , wherein the first threshold is a variable threshold.

4. The method of claim 1 , wherein the first threshold is pre-determined.

5. The method of claim 1 , wherein T1=5.

6. The method of claim 1 , wherein T2 is a predefined positive integer when the coding mode of the current block is an inter merge mode.

7. The method of claim 1 , wherein the maximally allowed number of motion candidates is based on at least one of a shape, size or coding mode of the current block.

8. The method of claim 6 , wherein the motion candidates list comprises a merge motion vector candidate list.

9. The method of claim 1 , wherein the current block is coded with an intra block copy mode in which prediction sample of the current block is generated by using at least a block vector pointing to another video block in a same picture containing the current block.

10. The method of claim 1 , wherein the table comprises one or more HMVP candidates derived from one or more video blocks that have been coded and indices of the HMVP candidates in the table is based on a sequence of addition of the HMVP candidates into the table.

11. The method of claim 1 , wherein at least one HMVP candidate is removed from the table due to addition of a new HMVP candidate into the table; wherein the at least one HMVP candidate is removed from the table to provide an empty entry in the table and HMVP candidates whose indices are greater than that of the at least one HMVP candidate are moved forward to fill the empty entry and the addition of the new HMVP candidate into the table is performed after the moving of the HMVP candidates.

12. The method of claim 1 , wherein the conversion includes encoding the current block into the bitstream.

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

14. An apparatus for coding 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, based on a first threshold (T1), a maximum number of history-based motion vector prediction (HMVP) candidates in an HMVP table to be checked, wherein the HMVP table includes one or more HMVP candidates, and wherein the one or more checked HMVP candidates in the HMVP table are used for constructing a motion candidates list;

make a decision regarding a selective checking of a number of the HMVP candidates in the HMVP table in an order, the number of the HMVP candidates in the HMVP table checked not exceeding the maximum number of HMVP candidates to be checked;

construct, based on the decision, the motion candidates list; and

perform, based on the motion candidates list, a conversion between a current block of a video and a bitstream of the video,

wherein checking the HMVP candidates in the HMVP table is terminated upon a determination that a number of available motion candidates in the motion candidates list, including added HMVP candidates, has reached a maximally allowed number of motion candidates in the motion candidates list minus a second threshold (T2), and wherein T2 is based on a coding mode of the current block.

15. The apparatus of claim 14 , wherein the maximum number of HMVP candidates to be checked is equal to the first threshold and the first threshold is a variable threshold.

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

determine, based on a first threshold (T1), a maximum number of history-based motion vector prediction (HMVP) candidates in an HMVP table to be checked, wherein the HMVP table includes one or more HMVP candidates, and wherein the one or more checked HMVP candidates in the HMVP table are used for constructing a motion candidates list;

make a decision regarding a selective checking of a number of the HMVP candidates in the HMVP table in an order, the number of the HMVP candidates in the HMVP table checked not exceeding the maximum number of HMVP candidates to be checked;

construct, based on the decision, the motion candidates list; and

perform, based on the motion candidates list, a conversion between a current block of a video and a bitstream of the video,

wherein checking the HMVP candidates in the HMVP table is terminated upon a determination that a number of available motion candidates in the motion candidates list, including added HMVP candidates, has reached a maximally allowed number of motion candidates in the motion candidates list minus a second threshold (T2), and wherein T2 is based on a coding mode of the current block.

17. 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:

determining, based on a first threshold (T1), a maximum number of history-based motion vector prediction (HMVP) candidates in an HMVP table to be checked, wherein the HMVP table includes one or more HMVP candidates, and wherein the one or more checked HMVP candidates in the HMVP table are used for constructing a motion candidates list;

making a decision regarding a selective checking of a number of the HMVP candidates in the HMVP table in an order, the number of the HMVP candidates in the HMVP table checked not exceeding the maximum number of HMVP candidates to be checked;

constructing, based on the decision, the motion candidates list; and

generating the bitstream based on the motion candidates list,

wherein checking the HMVP candidates in the HMVP table is terminated upon a determination that a number of available motion candidates in the motion candidates list, including added HMVP candidates, has reached a maximally allowed number of motion candidates in the motion candidates list minus a second threshold (T2), and wherein T2 is based on a coding mode of the current block.

18. The apparatus of claim 14 , wherein T2 is a predefined positive integer when the coding mode of the current block is inter merge mode.

19. The non-transitory computer-readable storage medium of claim 16 , wherein the maximum number of HMVP candidates to be checked is equal to the first threshold, and wherein the first threshold is a variable threshold.

20. The non-transitory computer-readable recording medium of claim 17 , wherein the maximum number of HMVP candidates to be checked is equal to the first threshold, and wherein the first threshold is a variable threshold.