Object Datagram — MoQT draft-08 §8.2.

An OBJECT_DATAGRAM carries a single object in a datagram.

An Object received in an OBJECT_DATAGRAM message has an Object Forwarding Preference = Datagram. To send an Object with Object Forwarding Preference = Datagram, determine the length of the header and payload and send the Object as datagram. In certain scenarios where the object size can be larger than maximum datagram size for the session, the Object will be dropped.

OBJECT_DATAGRAM {
  Track Alias (i),
  Group ID (i),
  Object ID (i),
  Publisher Priority (8),
  Extension Count (i),
  [Extension headers (...)],
  Object Payload Length (i),
  [Object Status (i)],
  Object Payload (..),
}

Figure 29: MOQT OBJECT_DATAGRAM

There is no explicit length field. The entirety of the transport datagram following Publisher Priority contains the Object Payload.