Pictures with mixed NAL unit types

An encoder comprising:

• one or more processors configured to:
• determine whether a picture contains a plurality of sub-pictures of different types;
• encode the sub-pictures of the picture into a plurality of video coding layer (VCL) network abstraction layer (NAL) units in a bitstream;
• and
• encode 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 NAL unit types in picture flag (mixed_nalu_types_in_pic_flag).

A method of storing a bitstream of a video into a non-transitory computer-readable recording medium, wherein the bitstream is generated by a method performed by a video processing apparatus, the method comprising:

• encoding a picture and a flag into the bitstream, wherein the picture is associated with a plurality of video coding layer (VCL) network abstraction layer (NAL) units, wherein the flag is a mixed NAL unit types in picture flag (mixed_nalu_types_in_pic_flag);
• and
• storing the bitstream in the non-transitory computer-readable recording medium,
• wherein 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, and
• wherein 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.