Encoder, decoder, encoding method, and decoding method

A non-transitory computer readable medium storing a bitstream,

• the bitstream including syntax information according to which a computer performs a decoding process including:
• in response to a determined number of sub blocks of a block being set to four, splits the block into four sub blocks, wherein,
• in response to a size of the block satisfying a block-size condition, splits the block into four sub blocks along a single direction, wherein the splitting includes,
• splitting the block along a vertical direction into four 8×8 sub blocks in response to the width of the block being larger than the height of the block and the size of the block being 32×8;
• and
• splitting the block along a horizontal direction into four 8×8 sub blocks in response to the height of the block being larger than the width of the block and the size of the block being 8×32;
• and
• in response to the size of the block not satisfying the block-size condition, splits the block into four sub blocks along the vertical and horizontal directions, wherein the splitting includes splitting the block along the vertical and horizontal directions into four 16×16 sub blocks in response to the width of the block being equal to the height of the block and the size of the block being 32×32;
• and
• decoding the sub blocks of the block.