5, inclusive, and in the range of 512 to 231 - 1, inclusive, may be used as determined by the application. Values of progressive_refinement id in the range of 256 to 511, inclusive, and in the range of 231 to 232 2, inclusive, are reserved for future use by ITU-TI ISO/IEC. Decoders encountering a value of progressive_refinement_i in the range of 256 to 511, inclusive, or in the range of 231 to 232 2, inclusive, shall ignore (remove from the bitstream and discard) it. num_refinement_steps_minus1 specifies the number of reference frames in the tagged set of consecutive coded pictures as follows: If num_refinement_steps_minus1 is equal to 0, the number of reference frames in the tagged set of consecutive coded pictures is unknown. Otherwise, the number of reference frames in the tagged set of consecutive coded pictures is equal to (num_refinement_steps_minus1+ num_refinement_steps_minus] shall be in the range of 0 to MaxFrameNum - 1, inclusive. D.2.18 Progressive refinement segment end SEI message semantics The progressive refinement segment end SEI message specifies the end of a set of consecutive coded pictures that has been labelled by use of a progressive refinement segment start SEI message as an initial picture followed by a sequence of one or more pictures of the refinement of the quality of the initial picture, and ending with the current picture. progressive_refinement_ic specifies an identification number for the progressive refinement operation. progressive_refinement_id shall be in the range of 0 to 232 2, inclusive. The progressive refinement segment end SEI message specifies the end of any progressive refinement segment previously started using a progressive refinement segment start SEI message with the same value of progressive_refinement_id Values of progressive_refinement id in the range of 0 to 255, inclusive, and in the range of 512 to 231 - 1, inclusive, may be used as determined by the application. Values of progressive_refinement id in the range of 256 to 511, inclusive, and in the range of 231