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 packaged by encoding the header using [BASE64] and then inserting that payload as the value of the Initialization data "initData" field in the catalog entry for that Track.