Motion candidate list construction for intra block copy (ibc) mode and non-ibc inter 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, for a first conversion between a first video block of a video and a bitstream of the video, a first motion candidate list in a first prediction mode, wherein in the first prediction mode, prediction samples are derived from blocks of sample values of a same slice as determined by block vectors, and wherein a maximum number of motion candidates in the first motion candidate list being equal to M1, and M1 being equal to or greater than 1;
• and
• construct, for a second conversion between a second video block of the video and the bitstream, a second motion candidate list in an inter merge prediction mode, wherein a maximum number of motion candidates in the second motion candidate list being equal to M2, and M2 being equal to or greater than 1;
• wherein at most L1 candidates in a first history-based motion vector predictor (HMVP) candidate table are inserted into the first motion candidate list, and wherein candidates in the first HMVP candidate table are arranged based on a sequence of addition of the candidates into the first HMVP candidate table, and L1 being equal to or greater than 0;
• wherein at most L2 candidates in a second HMVP candidate table are inserted into the second motion candidate list, and wherein candidates in the second HMVP candidate table are arranged based on a sequence of addition of the candidates into the second HMVP candidate table, and L2 being equal to or greater than 0, and
• wherein in a case that M1 is equal to M2, L1 is not equal to L2.

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

• construct, for a first conversion between a first video block of a video and a bitstream of the video, a first motion candidate list in a first prediction mode, wherein in the first prediction mode, prediction samples are derived from blocks of sample values of a same slice as determined by block vectors, and wherein a maximum number of motion candidates in the first motion candidate list being equal to M1, and M1 being equal to or greater than 1;
• and
• construct, for a second conversion between a second video block of the video and the bitstream, a second motion candidate list in an inter merge prediction mode, wherein a maximum number of motion candidates in the second motion candidate list being equal to M2, and M2 being equal to or greater than 1;
• wherein at most L1 candidates in a first history-based motion vector predictor (HMVP) candidate table are inserted into the first motion candidate list, and wherein candidates in the first HMVP candidate table are arranged based on a sequence of addition of the candidates into the first HMVP candidate table, and L1 being equal to or greater than 0;
• wherein at most L2 candidates in a second HMVP candidate table are inserted into the second motion candidate list, and wherein candidates in the second HMVP candidate table are arranged based on a sequence of addition of the candidates into the second HMVP candidate table, and L2 being equal to or greater than 0, and
• wherein in a case that M1 is equal to M2, L1 is not equal to L2.

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, for a first conversion between a first video block of a video and a bitstream of the video, a first motion candidate list in a first prediction mode, wherein in the first prediction mode, prediction samples are derived from blocks of sample values of a same slice as determined by block vectors, and wherein a maximum number of motion candidates in the first motion candidate list being equal to M1, and M1 being equal to or greater than 1;
• and
• constructing, for a second conversion between a second video block of the video and the bitstream, a second motion candidate list in an inter merge prediction mode, wherein a maximum number of motion candidates in the second motion candidate list being equal to M2, and M2 being equal to or greater than 1;
• generating the bitstream based on the first video block and the second video block;
• wherein at most L1 candidates in a first history-based motion vector predictor (HMVP) candidate table are inserted into the first motion candidate list, and wherein candidates in the first HMVP candidate table are arranged based on a sequence of addition of the candidates into the first HMVP candidate table, and L1 being equal to or greater than 0;
• wherein at most L2 candidates in a second HMVP candidate table are inserted into the second motion candidate list, and wherein candidates in the second HMVP candidate table are arranged based on a sequence of addition of the candidates into the second HMVP candidate table, and L2 being equal to or greater than 0, and
• wherein in a case that M1 is equal to M2, L1 is not equal to L2.