Prior Object ID Gap (Extension Header Type 0x3E) is a variable length integer
containing the number of Objects prior to the current Object that do not and
will never exist. This is equivalent to receiving an Object Does Not Exist
status for each skipped Object ID. For example, if the Original Publisher is
publishing Object 10 in Group 3 and knows it will never publish Objects 8 or 9
in this Group, it can include Prior Object ID Gap = 2. A Track is considered
malformed (see Section 2.4.2) if any of the following conditions are
detected:
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An Object contains more than one instance of Prior Object ID Gap.
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An Object has a Prior Object ID Gap larger than the Object ID.
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An endpoint receives an Object with a Prior Object ID Gap covering an Object it previously received.
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An endpoint receives an Object with an Object ID within a previously communicated gap.
This extension is optional, as publishers might not know the prior gap gize, or there may not be a gap. If Prior Object ID Gap is not present, the receiver cannot infer any information about the existence of prior objects (see Section 2.1).
This extension can be added by the Original Publisher, but MUST NOT be added by relays. This extension MUST NOT be modified or removed.
An Object MUST NOT contain more than one instance of this extension header.