Pictures with mixed NAL unit types

A method implemented in an encoder, the method comprising:

• determining whether a picture contains a plurality of sub-pictures of different types;
• encoding the sub-pictures of the picture into a plurality of video coding layer (VCL) network abstraction layer (NAL) units in a bitstream;
• encoding into the bitstream a flag set to a first value when a first NAL unit type value is the same for all VCL NAL units associated with the picture and set to a second value when the first NAL unit type value for VCL NAL units containing one or more of the sub-pictures of the picture is different than a second NAL unit type value for VCL NAL units containing one or more of the sub-pictures of the picture, wherein the flag is a mixed_nalu_types_in_pic_flag;
• and
• storing the bitstream for communication toward a decoder.

A decoder comprising:

• a receiver configured to receive a bitstream comprising a picture and a flag, wherein the picture is associated with a plurality of video coding layer (VCL) network abstraction layer (NAL) units, wherein the flag is a mixed_nalu_types_in_pic_flag;
• and
• a processor coupled to the receiver and configured to:
• determine a NAL unit type value is the same for all of the VCL NAL units of the picture when the flag is set to a first value;
• determine the VCL NAL units of the picture have a plurality of different NAL unit type values when the flag is set to a second value;
• and
• decode the picture based on the flag.

A method implemented in a decoder, the method comprising:

• receiving, by a receiver of the decoder, a bitstream comprising a plurality of sub-pictures associated with a picture and a flag, wherein the sub-pictures are contained in a plurality of video coding layer (VCL) network abstraction layer (NAL) units, wherein the flag is a mixed_nalu_types_in_pic_flag;
• determining, by a processor of the decoder, that a first NAL unit type value that is the same for all of the VCL NAL units associated with the picture when the flag is set to a first value;
• determining, by the processor, that a first NAL unit type value for a first set of the VCL NAL units containing one or more of the sub-pictures of the picture is different than a second NAL unit type value for a second set of the VCL NAL units containing one or more of the sub-pictures of the picture when the flag is set to a second value;
• and
• decoding, by the processor, one or more of the sub-pictures based on the first NAL unit type value or the second NAL unit type value.