Low memory design for multiple reference line selection scheme

A method for video encoding, the method comprising:

• receiving video data that comprises a plurality of blocks, including a current block;
• partitioning the current block to obtain a plurality of sub-blocks;
• and
• when a multiple reference line selection (MRLS) is to be applied for the current block:
• signaling a parameter in a coded video bitstream, the parameter indicating a reference line index corresponding to the MRLS;
• when a sub-block in the plurality of sub-blocks is located at a top boundary of the current block, using top-left values corresponding to an adjacent reference line to substitute values for top-left values of a non-adjacent reference line corresponding to the reference line index for the sub-block;
• and
• when the sub-block in the plurality of sub-blocks is not located at the top boundary, forgoing using the top-left values corresponding to the adjacent reference line to substitute values of the non-adjacent reference line corresponding to the reference line index for the sub-block.

A method of storing a video bitstream that is generated by a video encoding method into a non-transitory computer-readable storage medium, the method comprising:

• receiving a plurality of blocks of video data, the plurality of blocks including a current block;
• generating a parameter indicating a reference line index corresponding to a multiple reference line selection applied for the current block;
• coding information for the plurality of blocks of video data and the parameter into the video bitstream;
• and
• storing the video bitstream into the non-transitory computer-readable storage medium;
• wherein:
• the current block is partitioned to obtain a plurality of sub-blocks;
• when a sub-block in the plurality of sub-blocks is located at a top boundary of the current block, top-left values corresponding to an adjacent reference line are used to substitute values for top-left values of a non-adjacent reference line corresponding to the reference line index for the sub-block;
• and
• when the sub-block in the plurality of sub-blocks is not located at the top boundary, the top-left values corresponding to the adjacent reference line are not used to substitute values of the non-adjacent reference line corresponding to the reference line index for the sub-block.