A CMAF header is a sequence of CMAF constrained ISO BMFF boxes that do not reference any media samples, but are associated with a CMAF track and are necessary for initializing the decoding of the subsequent CMAF fragments.
The header for a given MOQT Track MUST be added to the catalog by generating an initDataList entry with a "type" of "inline", a "data" value of the header encoded using [BASE64] and an "id" which is unique across the initDataList items. That "id" value is then inserted as the value of an "initRef" property in all tracks which use that header for initialization.