The packets received by a hub from a camera are delivered with delay, but not in live mode.
For example, the current time is 2021-12-01 12:00:00, but the stream packets contain frames for 2021-12-01 11:59:40, which means that the accumulated delay is 20 seconds.
This happens when the network’s bandwidth is not big enough to transfer the traffic generated by the camera. In this case, the camera creates more packets than can be transferred over the network. All generated packets are placed into a queue, i.e. newly created packets will be sent not instantly, but only after the previous ones. So after some time, the queue will be gigantic and the newly created packets will be placed into the queue for a long time. The delay between creation and receiving of a packet is called accumulated delay.
Hub sends this event and immediately restarts the reading of the camera stream, it is needed to remove the delay. The event is emitted when the accumulated delay is bigger than 5 seconds.