Announce & Discover

Announcements notify which broadcasts exist and whether they are active. They are essential for track discovery in a session. You can send announcements from a moqt.Session by using the TrackMux.Publish, TrackMux.PublishFunc, or TrackMux.Announce methods on the associated moqt.TrackMux.

When a track is published on a moqt.TrackMux, it distributes Announcement to all listeners.

Announce Broadcasts

Broadcasts are announced when they are registered with the moqt.TrackMux. This can be done using the TrackMux.Announce method, or by using TrackMux.Publish or TrackMux.PublishFunc, which internally create the announcement.

    var mux *moqt.TrackMux
    var sess *moqt.Session // Holds the mux

    // Register and announce a broadcast
    ann, end := NewAnnouncement(ctx, "/broadcast_path")
    mux.Announce(ann, trackHandler)
    defer end() // Cleanup when done

    // Or use Publish and PublishFunc (serves Announcement internally)
    mux.Publish(ctx, "/broadcast_path", trackHandler)
    mux.PublishFunc(ctx, "/broadcast_path", trackHandleFunc)

Discover Broadcasts

Peers can discover available broadcasts by specifying the prefix for the broadcast path they are interested in and listening for announcements.

To be able to listen for announcements with a specific prefix, use the Session.AcceptAnnounce method. This returns a moqt.AnnouncementReader, which allows you to read incoming announcements.

var sess *moqt.Session

ar, err := sess.AcceptAnnounce("/prefix/")
if err != nil {
    // Handle error
}

for {
    ann, err := ar.ReceiveAnnouncement(context.Background())
    if err != nil {
        // Handle error
        break
    }
    // Handle announcement
    fmt.Println("Broadcast:", ann.BroadcastPath())
    fmt.Println("HopIDs:", ann.HopIDs()) // List of relay hop IDs the announcement traversed
}