SCTE 35 Part 1
segment_num
segmentation_descriptor · Decimal
The position of this item within a collection, one-based when numbering is used and 0 when it is not. For chapters it numbers chapters; for the placement-opportunity and ad-block types it numbers breaks, while sub_segment_num numbers the items within a break (SCTE 35 clauses 10.3.3.13 and 10.3.3.14).