PUBLISH — MoQT draft-20 §10.11.

The publisher sends PUBLISH as the first message on a new bidirectional stream to initiate a subscription for a Track. The receiver verifies the publisher is authorized to publish this track.

PUBLISH Message {
  Type (vi64) = 0x1D,
  Length (16),
  Request ID (vi64),
  Track Namespace (..),
  Track Name Length (vi64),
  Track Name (..),
  Track Alias (vi64),
  Number of Parameters (vi64),
  Parameters (..) ...,
  Track Properties (..),
}

Figure 14: MOQT PUBLISH Message

Request ID: See Section 10.1.
Track Namespace: Identifies a track's namespace as defined in (Section 2.4.1)
Track Name: Identifies the track name as defined in (Section 2.4.1).
Track Alias: The identifer used for this track in Subgroups or Datagrams (see Section 11.1).
Parameters: The parameters are defined in Section 10.2. Parameters such as FORWARD, GROUP_ORDER, SUBSCRIBER_PRIORITY, SUBGROUP_DELIVERY_TIMEOUT, OBJECT_DELIVERY_TIMEOUT, and LOCATION FILTER can appear in the Parameters of a PUBLISH to inform the Subscriber of the initial Subscription parameters. If the PUBLISH is the result of a SUBSCRIBE_TRACKS, the parameters are handled as described in Section 10.20.1, otherwise, they represent the publisher's initial settings for the subscription, which the subscriber can change.
Track Properties : A sequence of Properties. See Section 2.5.

A subscriber receiving a PUBLISH for a Track it does not wish to receive SHOULD send REQUEST_ERROR with error code UNINTERESTED, and abandon reading any publisher initiated streams associated with that subscription using a STOP_SENDING frame.

A publisher that sends the FORWARD parameter (Section 10.2.18) equal to 0 indicates that it will not transmit any objects until the subscriber sets the Forward State to 1. If the FORWARD parameter is omitted or equal to 1, the publisher will start transmitting objects immediately, possibly before PUBLISH_OK. Delivery starts at the Next Object relative to the Largest Object at the time the publisher begins sending.