Group IDs for a track MUST be unique and MUST increase monotonically. Within a continuous publishing session, each subsequent Group ID SHOULD increase by 1.
When a publisher restarts (e.g., after connectivity loss or encoder restart), it MUST ensure the new starting Group ID is greater than any previously published Group ID for that track. One approach is to use the current wall clock time in milliseconds since the Unix epoch as the starting Group ID.
If a publisher maintains state across a restart and knows the previous Group ID, it SHOULD signal the gap using the MOQT Prior Group ID Gap Extension header.