MIXED NAL UNIT TYPE BASED-VIDEO ENCODING/DECODING METHOD AND APPARATUS, AND METHOD FOR TRANSMITTING BITSTREAM

1 . An image decoding method performed by an image decoding apparatus, the image decoding method comprising:

obtaining video coding layer (VCL) network abstraction layer (NAL) unit type information of a current picture from a bitstream;

determining a NAL unit type of each of a plurality of slices included in the current picture, based on the obtained VCL NAL unit type information; and

decoding the plurality of slices based on the determined NAL unit type,

wherein the current picture includes a first subpicture and a second subpicture having different NAL unit types, based on at least some of the plurality of slices having different NAL unit types,

wherein a NAL unit type of the second subpicture is determined based on a NAL unit type of the first subpicture,

wherein whether at least some of the plurality of slices have different NAL unit types is determined based on first information obtained from the bitstream,

wherein a first value of the first information specifies that at least some of the plurality of slices have different NAL unit types,

wherein a second value of the first information specifies that the plurality of slices have the same NAL unit type, and

wherein all slices included in a subpicture in the current picture have the same NAL unit type.

2 . The image decoding method of claim 1 , wherein the second subpicture has a NAL unit type other than IDR_W_RADL and CRA_NUT, based on the first subpicture having a NAL unit type equal to IDR_N_LP.

3 . The image decoding method of claim 2 , wherein the second subpicture follows the first subpicture in decoding order and output order.

4 . The image decoding method of claim 1 , wherein the plurality of slices have a NAL unit type other than GDR_NUT.

5 . The image decoding method of claim 1 , wherein the second subpicture has a NAL unit type other than RADL_NUT and RASL_NUT, based on the first subpicture having a NAL unit type equal to one of IDR_W_RADL, IDR_N_LP, or CRA_NUT.

6 . The image decoding method of claim 1 , wherein the current picture has a picture type other than an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture.

7 . An image encoding method performed by an image encoding apparatus, the image encoding method comprising:

partitioning a current picture into one or more subpictures;

determining a network abstraction layer (NAL) unit type of each of a plurality of slices included in the one or more subpictures; and

encoding the plurality of slices based on the determined NAL unit type,

wherein the current picture includes a first subpicture and a second subpicture having different NAL unit types, based on at least some of the plurality of slices having different NAL unit types,

wherein a NAL unit type of the second subpicture is determined based on a NAL unit type of the first subpicture,

wherein first information specifying whether at least some of the plurality of slices have different NAL unit types is encoded,

wherein a first value of the first information specifies that at least some of the plurality of slices have different NAL unit types,

wherein a second value of the first information specifies that the plurality of slices have the same NAL unit type, and

wherein all slices included in a subpicture in the current picture have the same NAL unit type.

8 . The image encoding method of claim 7 , wherein the second subpicture has a NAL unit type other than IDR_W_RADL and CRA_NUT, based on the first subpicture having a NAL unit type equal to IDR_N_LP.

9 . The image encoding method of claim 8 , wherein the second subpicture follows the first subpicture in decoding order and output order.

10 . The image encoding method of claim 7 , wherein the plurality of slices have a NAL unit type other than GDR_NUT.

11 . The image encoding method of claim 7 , wherein the second subpicture has a NAL unit type other than RADL_NUT and RASL_NUT, based on the first subpicture having a NAL unit type equal to one of IDR_W_RADL, IDR_N_LP, or CRA_NUT.

12 . The image encoding method of claim 7 , wherein the current picture has a picture type other than an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture.

13 . A method of transmitting a bitstream generated by an image encoding method, the image encoding method comprising:

partitioning a current picture into one or more subpictures;

determining a network abstraction layer (NAL) unit type of each of a plurality of slices included in the one or more subpictures; and

encoding the plurality of slices based on the determined NAL unit type,

wherein the current picture includes a first subpicture and a second subpicture having different NAL unit types, based on at least some of the plurality of slices having different NAL unit types,

wherein a NAL unit type of the second subpicture is determined based on a NAL unit type of the first subpicture,

wherein first information specifying whether at least some of the plurality of slices have different NAL unit types is encoded,

wherein a first value of the first information specifies that at least some of the plurality of slices have different NAL unit types,

wherein a second value of the first information specifies that the plurality of slices have the same NAL unit type, and

wherein all slices included in a subpicture in the current picture have the same NAL unit type.