Encoder, decoder, encoding method, and decoding method

A decoder comprising:

• circuitry;
• and
• memory coupled to the circuitry,
• wherein, in operation, the circuitry:
• reads, from a bitstream, a parameter indicating whether a multilayer is allowed and first identifiers respectively identifying respective layers of respective network abstraction layer (NAL) units included in an encoded video sequence;
• and
• performs a single layer decoding process on the NAL units in a state in which the first identifiers respectively corresponding to the NAL units are set to an identical value indicating a layer, when the parameter indicates that the multilayer is not allowed.

A non-transitory medium storing a bitstream,

• the bitstream including a parameter indicating whether a multilayer is allowed, first identifiers respectively identifying respective layers to which respective network abstraction layer (NAL) units belong, and the NAL units,
• wherein the bitstream is parsed by a decoder,
• the first identifiers are set to an identical value indicating a layer, when the parameter indicates that the multilayer is not allowed, and
• the NAL units are to undergo a single layer decoding process, according to the parameter and the first identifiers, the NAL units belonging to an encoded video sequence.