METHODS AND SYSTEMS FOR CONSTRUCTING MERGE CANDIDATE LIST INCLUDING ADDING A NON- ADJACENT DIAGONAL SPATIAL MERGE CANDIDATE

1 . An encoder for providing an encoded bitstream, the bitstream being decodable by a compatible decoder, the bitstream including a coded picture partitioned into an array of coded blocks, one of the blocks being a current block, wherein the current block being a symmetric block, the decoder being configured to:

receive the bitstream;

construct for the current block a merge list of motion vector candidates, the merge list having a fixed number of candidates;

the constructing comprising:

evaluate a plurality of candidates from blocks spatially adjacent to the symmetric current block, and, if available, add the spatially adjacent candidates to the merge list;

if the number of spatially adjacent candidates added to the merge list is less than the fixed number, evaluate, according to a predetermined order, at least one candidate from a spatially non-adjacent block, at least one temporal candidate, a candidate derived from two other candidates, and a zero motion vector candidate; and

if available, add these candidates to the merge list until the number of candidates in the merge list equals the fixed number, wherein the candidate from a spatially non-adjacent block has a higher priority for inclusion in the merge list than the candidate derived from two other candidates and the zero motion vector candidate and wherein one or more of the spatially adjacent candidates are unavailable so that the number of spatially adjacent candidates added to the list is less than the fixed number, one unavailable spatially adjacent candidate being an asymmetric block, and wherein the spatially non-adjacent block is in the same row of CTU as the current block; and

decode the current block using the constructed merge list.

2 . The encoder of claim 1 wherein the asymmetric unavailable spatially adjacent candidate is an above left spatially adjacent candidate.

3 . The encoder of claim 1 wherein a below left spatially adjacent candidate is asymmetric and unavailable.

4 . A method of transmitting an encoded bitstream decodable by a compatible decoder, comprising:

encoding a bitstream including a coded picture partitioned into an array of coded blocks, one of the blocks being a current block, wherein the current block being a symmetric block;

transmitting the encoding bitstream over a channel to a compatible decoder, the decoder being configured to:

receive the bitstream;

construct for the current block a merge list of motion vector candidates, the merge list having a fixed number of candidates;

the constructing comprising:

evaluate a plurality of candidates from blocks spatially adjacent to the symmetric current block, and, if available, add the spatially adjacent candidates to the merge list;

if the number of spatially adjacent candidates added to the merge list is less than the fixed number, evaluate, according to a predetermined order, at least one candidate from a spatially non-adjacent block, at least one temporal candidate, a candidate derived from two other candidates, and a zero motion vector candidate; and

if available, add these candidates to the merge list until the number of candidates in the merge list equals the fixed number, wherein the candidate from a spatially non-adjacent block has a higher priority for inclusion in the merge list than the candidate derived from two other candidates and the zero motion vector candidate and wherein one or more of the spatially adjacent candidates are unavailable so that the number of spatially adjacent candidates added to the list is less than the fixed number, one unavailable spatially adjacent candidate being an asymmetric block, and wherein the spatially non-adjacent block is in the same row of CTU as the current block; and

decode the current block using the constructed merge list.

5 . A decoder having circuitry configured to:

receive a bitstream including a coded picture partitioned into an array of coded blocks including a first coded block and a second coded block, and signalling information indicating the first block is decoded using a merge mode and the second block is decoded without using a merge mode, the second block being an intra-predicted block,

construct for the first block a merge list of motion vector candidates, the merge list having a fixed number of candidates;

the constructing comprising:

evaluate a plurality of candidates from blocks spatially adjacent to the first block, and, if available, add the spatially adjacent candidates to the merge list;

if the number of spatially adjacent candidates added to the merge list is less than the fixed number, evaluate, according to a predetermined order,

at least one candidate from a spatially non-adjacent block, at least one temporal candidate, a candidate derived from two other candidates, and a zero motion vector candidate; and

if available, add these candidates to the merge list until the number of candidates in the merge list equals the fixed number, wherein the candidate from a spatially non-adjacent block has a higher priority for inclusion in the merge list than the candidate derived from two other candidates and the zero motion vector candidate and wherein one or more of the spatially adjacent candidates are unavailable so that the number of spatially adjacent candidates added to the list is less than the fixed number, one unavailable spatially adjacent candidate being an asymmetric block, and wherein the spatially non-adjacent block is in the same row of CTU units as the first block;

decode the first block using the constructed merge list; and

decode the second block without constructing a merge list of motion vector candidates and using intra-prediction.