e P (P slice) B (B slice) I (I slice) SP (SP slice) SI (SI slice) P (P slice) B (B slice) I (I slice) SP (SP slice) SI (SI slice) When slice type has a value in the range 5..9, it is a requirement of bitstream conformance that all other slices of the current coded picture shall have a value of slice_type equal to the current value of slice_type or equal to the current value of slice_type minus 5. NOTE 1 - Values of slice type in the range 5..9 can be used by an encoder to indicate that all slices of a picture have the same value of (slice_type % 5). Values of slice ty in the range 5..9 are otherwise equivalent to corresponding values in the range 0..4. When nal_unit_type is equal to 5 (IDR picture), slice_type shall be equal to 2, 4, 7, or 9. When max num ref frames is equal to 0, slice_type shall be equal to 2, 4, 7, or 9. pic_parameter_set_i specifies the picture parameter set in use. The value of pic_parameter_set_id shall in the range of 0 to 255, inclusive. colour plane id specifies the colour plane associated with the current slice RBSP when separate_colour_plane_flag is equal to 1. The value of colour_plane_id shall be in the range of 0 to 2, inclusive. colour_plane_id equal to 0, 1, and 2 correspond to the Y, Cb, and Cr planes, respectively. NOTE 2 - There is no dependency between the decoding processes of pictures having different values of colour_plane_id. frame num is used as an identifier for pictures and shall be represented by log2_max_frame_num_minus4+4 bits in the bitstream. frame_num is constrained as follows: The variable PrevRefFrameNum is derived as follows: Rec. ITU-T H.264 (01/2012) If the current picture is an IDR picture, PrevRefFrameNum is set equal to 0. Otherwise (the current picture is not an IDR picture), PrevRefFrameNum is set as follows: If the decoding process for gaps in frame num specified in clause 8.2.5.2 was invoked by the decoding process for an access unit that contained a non-reference picture that followed the previous access unit in decoding order that contained a referen