SCTE 104/35 Codex

A UPID, or Unique Program Identifier, is the value inside a segmentation descriptor that says which piece of content a boundary refers to. Its segmentation_upid_type selects the scheme, such as Ad-ID for spots, EIDR or ISAN for programs, or a plain URI, and the type also fixes how the bytes are read. Two container types stand apart: an MPU carries a vendor-defined private identifier, and a MID packs several UPIDs of different types into one descriptor.