SCTE 104/35 Codex

An avail is an opportunity the network gives a distributor to insert local content into a program. Two splice_insert fields position each one: avail_num says which avail this is within the program, and avails_expected states how many avails the program is expected to carry, so a downstream system can confirm its count matches the network's and recover if a message is missed or arrives out of order. avail_num can legitimately exceed avails_expected, for example when a live event runs over its allotted time and the provider signals extra avails during the overrun. Non-zero avail numbers must not be reused within a program, since that would make two avails ambiguous. These fields carry meaning only in an SCTE 118 Tier 2 workflow; systems that are not Tier 2 ignore them.